Chapter 20. The Knee

At the completion of this chapter, the reader will be able to:

1. Describe the anatomy of the joint, ligaments, muscles, and blood and nerve supply that comprise the knee joint complex.

2. Describe the biomechanics of the tibiofemoral and patellofemoral joints, including the forces involved with closed-chain and open-chain activities, the open- and close-packed positions, normal and abnormal joint barriers, force couples, and joint stabilizers.

3. Describe the purpose and components of an examination for the knee joint complex.

4. Perform a detailed examination of the knee joint complex, including palpation of the articular and soft tissue structures, specific passive and active mobility tests, stability tests, and special tests.

5. Understand the purpose of muscle function testing and extrapolate information from the findings.

6. Describe the significance of muscle imbalance in terms of functional muscle performance.

7. Outline the significance of the key findings from the history, the tests and measures of the knee complex, and establish a diagnosis.

8. Describe the common pathologies of the knee joint complex and their relationship to impairment.

9. Develop self-reliant intervention strategies based on clinical findings and established goals.

10. Apply active and passive techniques to the knee joint complex and its surrounding structures, using the correct intensity and duration.

11. Evaluate intervention effectiveness to progress or modify the intervention.

12. Plan an effective home program, and instruct the patient in this program.

13. Help the patient to develop self-reliant intervention strategies.

The knee joint complex is extremely elaborate and includes three articulating surfaces, which form two distinct joints contained within a single-joint capsule: the patellofemoral and tibiofemoral joints. Anatomically and biomechanically the tibiofemoral joint and the patellofemoral joint can be considered as separate entities, in much the same way as the craniovertebral joints are when compared with the rest of the cervical spine. In 15–20% of the population, an accessory sesamoid bone occurring in the gastrocnemius, the fabella, is present as part of the knee joint complex.1,2 The fabella, when present, articulates with the lateral femoral condyle and is hence an articular sesamoid.

The knee is one of the most commonly injured joints in the body. The types of knee injuries seen clinically can be generalized into the following categories:

• Unspecified sprains or strains, and other minor injuries, including overuse injuries
• Contusions
• Meniscal or ligamentous injuries

It is important that the clinician be familiar with the diagnostic and therapeutic procedures appropriate for all of the categories of injury. It is also important that the clinician have a good understanding of differential diagnosis as thigh, knee, and calf pain can result from a broad spectrum of conditions.

The tibiofemoral joint consists of the distal end of the femur and the proximal end of the tibia (Fig. 20-1). The tibiofemoral joint has great demands placed on it in terms of both stability and mobility. The femur is the largest bone in the body and represents approximately 25% of a person's height.3 Its distal aspect (Fig. 20-1) is composed of two femoral condyles that are separated by an intercondylar notch or fossa. The intercondylar notch serves to accept the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL).

The femoral condyles (see Fig. 20-1) project posteriorly from the femoral shaft. The smaller lateral femoral condyle is ball-shaped and faces outward, whereas the elliptical-shaped medial femoral condyle faces inward. The lateral condyle serves as the origin of the popliteus, whereas the lateral epicondyle serves as the origin for the lateral head of the gastrocnemius and the lateral collateral ligament (LCL). The medial epicondyle (see Fig. 20-1) serves as the insertion site for the adductor magnus, the medial head of the gastrocnemius, and the medial collateral ligament (MCL).

The anteroposterior length of the adult medial femoral condyle is on average 1.7 cm greater than that of its lateral counterpart, resulting in an increased length of the articular surface on the medial femoral condyle as compared with that of the lateral femoral condyle.5 Thus, the articulating surfaces are asymmetric, yet work in unison.2 The distal and the posterior portion of the femoral condyles articulate with the tibia.

The proximal tibia (see Fig. 20-2) is composed of two plateaus separated by the intercondylar eminence, including the medial and lateral tibial spines.6 The tibial plateaus are concave in a mediolateral direction. In the anteroposterior direction, the medial tibial plateau is also concave, whereas the lateral is convex, producing more asymmetry and an increase in lateral mobility. The medial plateau has a surface area that is approximately 50% greater than that of the lateral plateau, and its articular surface is three times thicker.7 The concavity of the tibial plateaus is accentuated by the presence of the menisci (see later).

The patellofemoral joint is a complex articulation, dependent on both dynamic and static restraints for its function and stability.

The patella (Fig. 20-1), a ubiquitous sesamoid bone found in birds and mammals, plays an important role in the biomechanics of the knee. Its articular anatomy is uncomplicated: it is a very hard, triangular-shaped bone, situated in the intercondylar notch and embedded in the tendon of the quadriceps femoris muscle above and the patellar tendon below. The thickness of the patella varies considerably, attaining a maximum height of 2–2.5 cm (0.77–1 inch) at its central portion.8 The posterior surface of the patella can include up to seven facets. A smaller facet, known as the odd facet, exists medially and is delineated by a second vertical ridge.9 These concave medial and lateral facets are separated by a vertical ridge and are covered with aneural hyaline cartilage, the thickest cartilage in the body (up to 7-mm thick).8 The articular cartilage of the patella is unique because it lacks conformity with the underlying bone.10 The hyaline cartilage, here as elsewhere, functions to minimize the friction that occurs at the functional contact areas of the joint surfaces.

Radiographic and cadaver studies have classified the patella into four types based on the size and shape of these lateral and medial facets.11

The patellar surface of the femur is divided into medial and lateral facets that closely correspond to those on the posterior surface of the patella.12 The patellofemoral joint functions to13

• provide the articulation with low friction;
• protect the distal aspect of the femur from trauma and the quadriceps from attritional wear;
• improve the cosmetic appearance of the knee;
• improve the moment arm (distance between the center of gravity and the center of rotation) of the quadriceps. This is achieved by elevating the quadriceps femoris muscle from the center of knee rotation. This increases the efficiency of the quadriceps muscle and provides it with leverage for extending the leg. The patellar contribution to the knee extensor moment arm increases with increasing amounts of knee extension;
• decrease the amount of anteroposterior tibiofemoral shear stress placed on the joint.

The capsule of the knee joint complex is composed of a thin, strong fibrous membrane and is the largest synovial capsule in the body. The capsule ascends anteriorly approximately 2 finger breadths above the patella to form the suprapatellar pouch. Posteriorly, it ascends to the origins of the gastrocnemius. Inferiorly, the capsule attaches along the edges of the articulating surfaces of the tibial plateaus, with the exception of the intercondylar eminence, and a small portion of the anterior intercondylar region.14 A synovial membrane lines the inner portion of the knee joint capsule. By lining the joint capsule, the synovial membrane excludes the cruciate ligaments from the interior portion of the knee joint, making them extrasynovial yet intra-articular.

The articularis genu, located superior to the patella, is thought to function to retract the knee capsule during knee extension. Thus, it serves a similar function as the anconeus in the elbow.

The proximal, or superior, tibiofibular joint (see Fig. 20-1) is an almost plane joint with a slight convexity on the oval tibial facet and a slight concavity of the fibular head. The joint is located below the tibial plateau on the lateral condyle of the tibia. The tibial articulating facet faces laterally, posteriorly, and inferiorly. Although the joint is often described as a simple, synovial, modified ovoid, it functions as a modified sellar when combined with the distal, or inferior, tibiofibular joint (see Chap. 21).

The joint capsule of the proximal tibiofibular joint complex is thicker anteriorly than posteriorly and, in 10% of the population, the synovium is continuous with that of the knee joint.15 The joint receives support from anterior and posterior ligaments, and an interosseous membrane. The interosseous membrane attaches between the medial border of the fibula and the lateral border of the tibia, providing attachment to the deep anterior and posterior muscles of the leg. The majority of its fibers pass obliquely in an inferior and lateral direction.

The proximal tibiofibular joint has more motion than its distal partner. The motion occurring at the proximal joint consists of two glides, one in a superoinferior direction and the other in an anteroposterior direction.7 These motions are possible because of the orientation of the joint line, which also facilitates an osteokinematic spin of the fibula. The motion at this joint can be decreased by articular fibrosis or by soft tissue restraints; the biceps femoris can pull or hold it posteriorly, whereas the tibialis anterior can pull or hold it anteriorly.

Although the capsular pattern of restriction for this joint is unclear, it is probably indicated by pain during an isometric contraction of the biceps femoris with the knee at 90 degrees of flexion. The close-packed position for this joint, equally debatable, is probably weight-bearing ankle dorsiflexion.

Both the tibia and fibula are vulnerable to fracture at the lower third of their shaft. Anterior joint subluxations occur at this joint as a result of medial knee joint strain or an inversion sprain of the ankle. Posterior joint subluxation can occur as a result of a lateral knee joint strain, but is often missed because of the more serious ligament damage to the knee.

The nerve supply for this joint is provided by the common fibular (peroneal) and recurrent articular nerves. The joint receives its blood supply from a perforating branch of the fibular (peroneal) artery, and the anterior tibial artery.

The static stability of the knee joint complex depends on four major knee ligaments, which provide a primary restraint to abnormal knee motion:

• Anterior cruciate (Fig. 20-1). Provides the primary restraint for anterior translation and medial rotation of the tibia on the femur and is a secondary restraint to valgus and varus rotation of the tibia.
• Posterior cruciate (see Fig. 20-1). Provides the primary restraint for posterior translation and medial rotation of the tibia on the femur and is a secondary restraint to valgus and varus rotation of the tibia.
• Medial (tibial) collateral (see Fig. 20-1). Provides the primary restraint for valgus and lateral rotation of the tibia, and is a secondary restraint to anterior and posterior translation of the tibia on the femur.
• Lateral (fibular) collateral (see Fig. 20-1). Provides the primary restraint for varus and lateral rotation of the tibia, and is a secondary restraint to anterior and posterior translation of the tibia on the femur.

Cruciate Ligaments

The two central intra-articular cruciate ligaments derive their name from the Latin word crucere (cross) because they cross each other (Fig. 20-1). Both the ACL and PCL lie in the center of the joint, and each are named according to their attachment sites on the tibia.15 The cruciate ligaments, which differ from those of other joints in that they restrict normal, rather than abnormal, motion, are the main stabilizing ligaments of the knee and restrain against anterior (ACL) and posterior (PCL) translations of the tibia on the femur. They also restrain against excessive internal and external rotation and varus movement of the tibia.16

The blood supply to the cruciate ligaments is largely provided from the middle and inferior geniculate branches of the popliteal artery. The cruciate ligaments are innervated by the posterior articular nerve, a branch of the posterior tibial nerve.20 The function of this nerve supply is questionable although it may serve as proprioceptive in nature.21 In addition, the cruciate ligaments contain mechanoreceptors, suggesting that disruption of the ligament structure can produce partial deafferentation of the joint.22 Evidence of a proprioceptive function of the ACL comes from extensive histologic observations demonstrating that the ACL appears to contain proprioceptive nerve endings.23,24 Indeed, Krauspe et al.,20 in single-fiber studies, identified a total of 26 mechanoreceptors of the cruciate ligament among 13 animals.

Although these cruciate ligaments function together, they are described separately.

Anterior Cruciate Ligament

The ACL is a unique structure and one of the most important ligaments to knee stability, serving as a primary restraint to anterior translation of the tibia relative to the femur, and a secondary restraint to both internal and external rotation in the non–weight-bearing knee.25–28 An injury to this ligament has terminated many a promising sports career.29,30

The ACL (see Fig. 20-1) is composed of a vast array of individual fascicles. These, in turn, are composed of numerous interlacing networks of collagen fibrils. The fascicles originate on the inner aspect of the lateral femoral condyle in the intercondylar notch and travel obliquely and distally through the knee joint.16 They enter the anterior intercondylar surface of the tibial plateau, where they partially blend with the lateral meniscus. As the fascicles of the ACL course through the knee joint and attach to their insertion sites, they fan out and give a slight spiral appearance to the ligament, a phenomenon that is more pronounced during knee flexion.31,32

The synovial tissue that enfolds the ACL consists of an intimal layer, facing the joint cavity, and a subsynovial layer.16 The subsynovial layer is in direct contact with the ACL and contains neurovascular structures. The ACL is considered intra-articular yet extrasynovial because of the posterior invagination of the synovial membrane.

Although the posterior articular nerve is the major nerve for the ACL, afferent fibers have also been demonstrated in the medial and lateral articular nerves. 33

Like all ligaments, the ACL behaves as a viscoelastic structure, allowing it to dissipate energy and to adjust its length and internal load distribution as a function of load history.34,35 This means that the normal ACL is capable of microscopic adjustments to internal stresses over time, thus influencing the laxity, stresses, and kinematics of the joint in subtle but potentially important ways.36 One anatomic factor that contributes to selective fiber recruitment during tensile loading is the specific location of the insertions of the ACL on the femur and the tibia. These differing insertion sites allow different fibers of the ACL to be recruited with every subtle three-dimensional change in the position of the joint.31,36–38

Butler et al.39 have shown that whatever the angle of knee flexion, the ACL absorbs nearly 90% of the force causing anterior translation. The anteromedial bundle of the ACL is taut in flexion, whereas in extension, the posterolateral fibers are stretched. These unique properties not only make the ACL the “crucial” ligament of the knee joint, but also increase its potential for injury.28,40,41

The tensile strength of the ACL is equal to that of the knee collaterals, but is half that of the PCL.42 Since its fibers are unyielding, forcing the ACL more than 5% beyond its resting length may result in rupture.28 Several factors can influence the amount of tension on the ACL.

• Compressive loading of the tibiofemoral joint, such as that occurs during weight-bearing, has been shown to reduce anteroposterior laxity and stiffen the joint when compared with the non–weight-bearing position.43 These changes appear to reflect the increased strain borne by the ACL during the transition from non–weight-bearing to weight-bearing.44 Thus, the popular belief in the beneficial effects of early weight-bearing and closed-kinetic chain exercises (CKCEs) following anterior cruciate reconstruction may be open to question (Table 20-1).44
• Stair-climbing exercises using exercise equipment such as the Stairmaster 4000PT (Randall Sports Medicine, Kirkland, WA) have been shown to produce moderate strain on the ACL compared with other rehabilitation activities.45
• The circumstances that cause the highest loads and strains on the ACL during daily function are36 quadriceps-powered extension of the knee, moving it from approximately 40 degrees of flexion to full extension; hyperextension of the knee; excessive internal tibial rotation; or excessive varus or valgus stress on the tibia if a collateral ligament is torn.

Both estimates46,47 and measurements25,26 have shown that the maximum measured strain differential in the ACL is approximately 5% during any rehabilitation exercise.36,48 This strain represents only approximately one-quarter of the failure strain of the normal ACL, suggesting that these exercises load the normal ACL to only a small fraction of its failure capacity.34,36,38

Posterior Cruciate Ligament

The PCL attaches posteriorly to the insertion of the posterior horns of the lateral and medial menisci on the posterior part of the posterior intercondylar fossa of the tibia.49 From here, the PCL extends obliquely medially, anteriorly, and superiorly to attach to the lateral surface of the medial femoral condyle (see Fig. 20-1). Overall, the ligament is wider at its femoral origin and narrowest near the tibial insertion.50 The PCL is covered by synovial lining and is therefore considered to be extrasynovial yet intra-articular.

Information regarding the biomechanical function of the PCL is scant compared with that of the ACL. It is known that the PCL is 50% thicker and has twice the tensile strength of the ACL.51 The PCL is more vertical in extension and horizontal in flexion.52 Like the ACL, the PCL consists of two bundles: anterior lateral and posterior medial. Overall, the ligament is most taut with further flexion of the knee.53 Specifically, the anterior lateral bundle is taut in flexion, while the posterior medial bundle is taut in extension. According to Butler et al.,39 the PCL provides 90–95% of the total restraint to posterior translation of the tibia on the femur, with the remainder being provided by the collateral ligaments, posterior portion of the medial and lateral capsules, and the popliteus tendon. The contribution percentage resisting posterior translation decreases as the knee extends. The PCL is significantly loaded if a posteriorly directed force is applied to the tibia when the knee is flexed to 90 degrees or greater while in neutral rotation.54 If the same force is applied to the tibia when the knee is in terminal extension, the load on the PCL is not increased.54 This is contrary to the popular belief that hyperextension of the knee is the mechanism of injury of the PCL. The PCL also restrains internal rotation of the tibia on the femur and helps prevent posterior-medial instability at the knee.55

Other functions of the PCL include acting as a secondary restraint to external rotation of the tibia on the femur at 90 degrees of flexion,56 assisting with a rolling/gliding mechanism of the tibiofemoral joint, and resisting varus/valgus forces at the knee after the collateral ligaments have failed.

A significant force is needed to tear the PCL. Thus, tears of the PCL are usually the result of severe contact injuries that often occur in traumatic situations, such as a dashboard injury during a motor vehicle accident.

In concert with the PCL are the anterior and posterior meniscofemoral ligaments, which comprise approximately 22–50% of the cross-sectional area of the PCL.50,57 Although these ligaments arise from the common PCL origin they are distinct structures having different insertion sites.58 Both are named with respect to the orientation to the PCL (see “Lateral Meniscus” section). Since the insertion site of the meniscofemoral ligaments are different from that of the PCL, if a midsubstance tear of the PCL occurs, it is possible that one or both of the meniscofemoral ligaments may remain intact.59

Medial Collateral Ligament

Both the MCL and the LCL are considered to be extra-articular ligaments.

The MCL, or tibial collateral ligament (see Fig. 20-1), develops as a thickening of the medial joint capsule.60 It can be subdivided into a superficial band and a deep band.

• The superficial band is a thick, flat band, and has a fan-like attachment proximally on the medial femoral condyle, just distal to the adductor tubercle, from which it extends to the medial surface of the tibia approximately 6 cm below the joint line, covering the medial inferior genicular artery and nerve.61 The superficial band blends with the posteromedial corner of the capsule and, when combined, is referred to as the posterior oblique ligament.62 The superficial band is separated from the deep layer of the ligament by a bursa. Since the superficial band is farther from the center of the knee, it is the first ligament injured when a valgus stress is applied.63
• The deep band (medial capsular ligament) is a continuation of the capsule. It blends with the medial meniscus and consists of an upper meniscofemoral portion and a lower meniscotibial portion.

The anterior fibers of the MCL are taut in flexion and can be palpated easily in this position. The posterior fibers, which are taut in extension, blend intimately with the capsule and with the medial border of the medial meniscus, making them difficult to palpate.

Information regarding the biomechanical function of the collateral ligaments is quite scarce compared with that of the ACL. It would appear that the MCL is the primary stabilizer of the medial side of the knee against valgus forces, and external rotation of the tibia, especially when the knee is flexed.64 Grood et al.65 determined that the MCL was the primary restraint, providing 57% and 78% of the total restraining moment against valgus force at 5 and 25 degrees of flexion.66

Lateral Collateral Ligament

The LCL, or fibular collateral ligament (see Fig. 20-1), arises from the lateral femoral condyle and runs distally and posteriorly to insert into the head of the fibula. The LCL forms part of the so-called arcuate-ligamentous complex. This complex also comprises the biceps femoris tendon, iliotibial tract, and the popliteus.

The cord-like LCL develops independently, and remains completely free from the joint capsule and the lateral meniscus. It is separated from these structures by the popliteus tendon, and straddled by the split tendon of the biceps femoris. The LCL can be divided into three parts:

1. Anterior. This part consists of the joint capsule.

2. Middle. This part is considered to be part of the iliotibial band (ITB) and covers the capsular ligament.

3. Posterior. This Y-shaped portion of the ligament is part of the arcuate-ligamentous complex, which supports the posterior capsule.67,68

The main function of the LCL is to resist varus forces. It offers the majority of the varus restraint at 25 degrees of knee flexion,69,70 and in full extension.

Some structures in the knee clearly augment the functions of the ACL and the PCL. These structures are known as secondary restraints.36 The secondary restraints include the structures in the posterolateral and posteromedial corners of the knee, which serve to control anterior tibial translation relative to the femur.36,54,71,72

Dynamic stability synergistic to the PCL is provided by unopposed contraction of the quadriceps complex, which increases anterior tibial translation. Conversely, an isolated contraction of the hamstrings results in a posterior translation of the tibia, which is synergistic to the ACL. Cocontraction of the hamstrings and the quadriceps has been theorized to minimize tibial translation in either direction.36 The popliteus muscle–tendon complex (PMTC) contributes to both static and dynamic posterolateral knee joint stabilization.73 During concentric activation, the popliteus internally rotates the tibia on the femur. During eccentric activation, it serves as a secondary restraint to tibial external rotation on the femur (see “Popliteus” section).74

The knee joint is also strengthened externally by the patellar ligament, oblique popliteal ligaments, and the fabella.

• The patellar ligament, or patellar tendon, lies in the thickened portion of the quadriceps femoris tendon between the top of the patella and the tibia (Fig. 20-1). The patellar ligament strengthens the anterior portion of the knee joint and prevents the lower leg from being flexed excessively.
• The oblique popliteal ligament, located on the posterior surface of the knee joint, is a dense thickening in the posterior capsule made up of a continuation of the popliteal tendon and part of the insertion of the semimembranosus.65 It arises posterior to the medial condyle of the tibia and extends superomedially to attach to the posterior fibrous capsule. The oblique popliteal ligament provides reinforcement to the lateral capsule, limits anteromedial rotation of the tibia, and prevents hyperextension of the knee.16
• The fabella is located in the posterolateral corner of the knee and may be osseous or cartilaginous in makeup. When the fabella is present, there is a fabellofibular ligament, which courses superiorly and obliquely from the lateral head of the gastrocnemius to the fibular styloid.68 The fabellofibular ligament helps prevent excessive internal rotation of the tibia and adds further ligamentous support on the lateral and posterolateral aspects of the knee.75 Seebacher et al. found through dissection that the arcuate ligament was quite large in the absence of a fabella.1

The crescent-shaped lateral and medial menisci (Fig. 20-2), attached on top of the tibial plateaus, lie between the articular cartilage of the femur and the tibia. The knee menisci, once described as “the functionless remains of leg muscles,”76 are now recognized as being integral to normal knee function. The blood supply of the meniscus, which is key to successful meniscal repair, comes from the perimeniscal capsular arteries, which are branches of the lateral, medial, and middle genicular arteries.16 The outer 25% of the lateral meniscus (with the exception of the posterolateral corner of the lateral meniscus adjacent to the popliteus tendon) and the outer 30% of the medial menisci are vascularized, giving these areas the potential for healing.77 The remaining inner portions of the menisci are considered avascular. Despite the lack of vascularity to the inner portions, tears involving the avascular zone may heal. This healing capacity may be improved with the addition of a fibrin clot or with such techniques as trephination.78,79

Medial Meniscus

The semilunar or U-shaped medial meniscus (see Fig. 20-2), with the wider separation of its anterior and posterior horns, is larger and thicker than its lateral counterpart and sits in the concave medial tibial plateau.80 The medial meniscus is wider posteriorly than anteriorly. It is attached to the anterior and posterior tibial plateau by coronary ligaments. These ligaments connect the outer meniscal borders with the tibial edge and restrict movement of the meniscus. The medial meniscus also has an attachment to the deeper portion of the MCL and the knee joint capsule. The horns of the medial meniscus are further apart than those of the lateral, which makes the former nearly semilunar and the latter almost circular (see Fig. 20-2). The posterior horn of the medial meniscus receives a piece of the semimembranosus tendon.

The transverse genicular ligament serves as a link between the lateral and medial menisci.

Lateral Meniscus

The lateral meniscus, which forms a C-shaped incomplete circle,80 sits atop the convex lateral tibial plateau (see Fig. 20-2). It is smaller, thinner, and more mobile than its medial counterpart.

The lateral meniscus has an interesting relationship with the popliteus tendon, which supports it during knee extension and separates it from the joint (see later discussion).73

The periphery of the lateral meniscus attaches to the tibia, the capsule, and the coronary ligament, but not to the LCL. Two meniscofemoral ligaments, the ligaments of Humphrey and Wrisberg attach to the lateral meniscus.5

• The ligament of Humphrey, also known as the anterior meniscofemoral ligament, runs anteriorly to the PCL and inserts on the posterior aspect of the lateral meniscus.58
• The ligament of Wrisberg, also known as the posterior meniscofemoral ligament, runs posteriorly to the PCL to insert either into the superior/lateral aspect of the tibia, the posterior aspect of the lateral meniscus, or the posterior capsule.81

The meniscofemoral ligaments become taut with internal rotation of the tibia and help with stabilization of the meniscus.61

The lateral meniscus often is associated with the appearance of synovial-filled cysts, which may occur following a minor injury to the meniscus and produce a small internal tear. As fluid begins to congregate within this tear, it is pushed deeper and deeper into the meniscus. The swelling eventually produces a small bulge on the lateral aspect of the meniscus.

Menisci Function

The menisci assist in a number of functions, including load transmission, shock absorption, joint lubrication and nutrition, secondary mechanical stability (particularly the posterior horn of the medial meniscus that blocks anterior translation of the tibia on the femur),80 and the guiding of movements.82

Load Transmission

The meniscus is viscoelastic, with greater stiffness at higher deformation rates. Many studies have confirmed the role of the menisci in load transmission by showing decreased contact area and increased peak articular stresses following partial or total meniscectomy.83–85 The lateral meniscus carries 70% of the compressive load in the lateral compartment, compared with just 40% by the medial meniscus in its respective compartment.80,86–88 By converting joint loading forces to radial-directed hoop stresses on their circumferential collagen fibers, and taking advantage of their viscoelastic nature, the menisci transmit 50–60% of the joint load when the knee is in extension, and 85–90% when the knee is in flexion.86–95

Shock Absorption

Because of their viscoelastic nature, the menisci are able to assist in shock absorption. During the normal gait pattern, the articular surface of the knee bears up to six times the body weight, with over 70% of that load borne by the medial tibial plateau.80,96 The medial tibial plateau bears most of this load during stance when the knee is extended, with the lateral tibial plateau bearing more of the much smaller loads imposed during the swing phase.96 This is compensated for by the fact that the medial tibial plateau has a surface area roughly 50% larger than the lateral plateau, and articular cartilage that is approximately three times thicker than the lateral articular cartilage.97

Joint Lubrication

The menisci assist in joint lubrication by helping to compress synovial fluid into the articular cartilage, which reduces frictional forces during weight-bearing. A meniscectomy increases the coefficient of friction within the knee, thereby increasing the stresses on the articular surfaces.100

Joint Stability

The menisci deepen the articulating surfaces of tibial plateaus. This increases the stability of the knee, especially during axial rotation and valgus–varus stresses.100–104

If the ACL is intact, the menisci do not significantly contribute to anteroposterior stability.43,105,106,107 However, in an ACL-deficient knee, the posterior horn of the medial meniscus functions as a secondary restraint to anteroposterior translation by wedging between the femur and the tibia.106,108 In contrast, the increased mobility of the lateral meniscus prevents it from contributing to anteroposterior stability.105 This difference helps to explain the higher incidence of medial meniscus tears seen in ACL-deficient knees.109

Guiding Movement

During flexion and extension of the knee, the menisci move posteriorly and anteriorly, respectively. The lateral meniscus has greater mobility because it does not attach to the LCL, and, as mentioned previously, its capsular attachment is interrupted by the passage of the popliteus tendon.73,110 During knee motion, the menisci move on the tibial plateau with the femoral condyles to maintain joint congruence.110 The femur, accompanied by the menisci, rolls anteriorly on the tibia during extension, and posteriorly during flexion (Fig. 20-3).100,110,111 Thompson et al.112 demonstrated that the mean anteroposterior excursion of the menisci during a 120-degree arc of motion was 5.1 mm at the medial meniscus, and 11.2 mm at the lateral. The inner sides of the menisci, which are attached by their horns to the tibial plateau, move with the tibia. As the body of each meniscus is fixed around the femoral condyle, they move with the femur. Therefore, during movements between tibia and femur, distortion of the menisci is inevitable.

• During flexion of the knee, the menisci move posteriorly. The medial meniscus is moved about 5 mm by the pull of the semimembranosus tendon, and the lateral meniscus is pulled about 11 mm by the popliteus, resulting in an external rotation of the tibia.
• During extension, the menisci move anteriorly.
• During external rotation of the tibia, the menisci will follow the displacement of the femoral condyles, which means that the medial meniscus is pushed posteriorly and the lateral meniscus is pulled anteriorly. During internal rotation, the opposite occurs. These rotations are conjunct, integral with flexion and extension, but can also be adjunct and independent, best demonstrated with the knee semiflexed. Conjunct external rotation of the tibia on the femur during the last stages of knee extension is part of a locking mechanism called the “screw home” mechanism, described later.
• The medial coronary ligament is stretched during external rotation of the tibia, whereas the lateral coronary ligament is stretched during internal rotation of the tibia.

There are a number of bursae situated in the soft tissues around the knee joint. The bursae serve to reduce friction and to cushion the movement of one body part over another.

Superficial and Deep Infrapatellar Bursae

The superficial infrapatellar bursa is located between the patellar tendon and the skin, whereas the deep infrapatellar bursa is located between the patellar tendon and the tibia.

Prepatellar Bursa

The prepatellar bursa is located between the skin and the anterior aspect of the patella.

Tibiofemoral Bursa

The tibiofemoral bursae consist of a bursa between the head of the gastrocnemius muscle and the joint capsule on both sides, a bursa between the LCL and both the biceps femoris and popliteus, and a bursa between the MCL and the femoral condyle. There are also a number of bursae between the various tendons of the pes anserinus and between the MCL and the superficial pes anserinus.

The bursae around the knee can have contact with each other and with the knee joint capsule.

Fat Pads

There are three fat pads located at the anterior knee: the quadriceps fat pad, the prefemoral fat pad, and the infrapatellar (Hoffa's) fat pad. The fat pads of the knee house neurovascular projections. The functions of the fat pads include the following:

• Synovial fluid secretion
• Joint stability
• Neurovascular supply
• Occupiers of dead space

Synovial plicae of the knee were first described in the beginning of the last century.113,114 Postmortem studies have shown plica to be present in 20–50% of knees,10,115,116 with the highest prevalence in individuals of Japanese descent.114,117–120

Synovial plica represents a remnant of the three separate cavities in the synovial mesenchyme of the developing knee. These cavities are supposed to coalesce into one cavity at the 12-week stage of fetal growth.121,122 The size and extent of this remnant depends on the degree of reabsorption.123

The three joints involved in the developing knee from which the remnants evolve are112

1. the joint between the fibular and the femur;

2. the joint between the tibia and the femur;

3. the joint between the patella and the femur.

The most common plica in the knee is called the anterior or inferior plica, or mucous ligament.121,124 This plica is represented by tape-like fold running from the fat pad to the intercondylar notch of the femur and overlying the ACL. The plicae to the medial and lateral sides of the patella, which run in a horizontal plane from the fat pad to the side of the patellar retinaculum, are referred to as the superomedial or superolateral plicae or the suprapatellar membrane, or the medial or lateral synovial shelf. 121

It has been suggested that symptomatic synovial plicae are one of the causes of anterior pain in the knee in children and adolescents.125–127

The wing-like retinacula of the knee are formed from structures in the first and second layers of the knee joint. The retinacula can be subdivided into the medial and the lateral retinacula for clinical examination and intervention purposes.128,129 The retinacula serve to connect the patella to a number of structures, including the femur, menisci, and tibia, both medially and laterally.9

The lateral retinaculum is the stronger and thicker of the two. It consists of two distinct layers of fibrous connective tissue: the superficial and deep retinacula. These structures are oriented longitudinally with the knee extended.129

• The superficial retinaculum consists of fibers from the vastus lateralis (VL) and the ITB.130
• The deep retinaculum consists of the lateral patellofemoral ligament, the deep fibers of the ITB, and the lateral patellotibial ligament.130 These structures connect the patella to the ITB and help prevent medial patellar excursion.131

Although partially located deep to the ITB, the lateral retinaculum is blended with the biceps femoris to form a so-called conjoint tendon.1,129 This relationship may explain why adaptively shortened hamstrings can lead to patellofemoral symptoms.9 It is also well established that adaptive shortening of the lateral retinaculum is a common finding in patellofemoral dysfunction.132–136

Given the fact that the medial retinaculum is thinner than the lateral retinaculum, it is not thought to be as significant to patella position and tracking as its lateral counterpart.

The major muscles that act on the knee joint complex are the quadriceps, the hamstrings (semimembranosus, semitendinosus, and biceps femoris), the gastrocnemius, the popliteus, and the hip adductors (Table 20-2).

Quadriceps

The four muscles that make up the quadriceps are the rectus femoris, the vastus intermedius, the VL, and the vastus medialis (Fig. 19-7). The quadriceps tendon represents the convergence of all four muscles tendon units, and it inserts into the anterior aspect of the superior pole of the patella. The quadriceps muscle group is innervated by the femoral nerve. The quadriceps muscles can act to extend the knee when the foot is off the ground, although more commonly, they work as decelerators, preventing the knee from buckling when the foot strikes the ground.137,138

Rectus Femoris

The rectus femoris (see Fig. 19-7), which originates at the anterior inferior iliac spine (AIIS) is the only quadriceps muscle that crosses the hip joint. The other quadriceps muscles originate on the femoral shaft. This gives the hip joint substantial significance with respect to the knee extensor mechanism in the examination and intervention.138 The line of pull of the rectus femoris, with respect to the patella, is at an angle of about 5 degrees with the femoral shaft138 (see Fig. 20-12).

Vastus Intermedius

The vastus intermedius (see Fig. 19-7) has its origin on the proximal part of the femur, and its line of action is directly in line with the femur.

Vastus Lateralis

The VL (Fig. 19-7) is composed of two functional parts: the VL and the vastus lateralis oblique (VLO).137 The VL has a line of pull of about 12–15 degrees to the long axis of the femur in the frontal plane, whereas the VLO has a pull of 38–48 degrees.138

Vastus Medialis

The vastus medialis (Fig. 19-7) is composed of two parts that are anatomically distinct137: the vastus medialis obliquus (VMO) and the vastus medialis proper, or longus (VML).139 The VML appears to have little biomechanical significance unlike its counterpart, the VMO.

Vastus Medialis Obliquus

The VMO arises from the adductor magnus tendon.140 The insertion site of the normal VMO is the medial border of the patella, approximately one-third to one-half of the way down from the proximal pole. If the VMO remains proximal to the proximal pole of the patella and does not reach the patella, there is an increased potential for malalignment.11

The vector of the VMO is medially directed, and it forms an angle of 50–55 degrees with the mechanical axis of the leg.137,140–142 The VMO is least active in the fully extended position143–145 and plays little role in extending the knee, acting instead to realign the patella medially during the extension maneuver. It is active in this function throughout the whole range of extension.

According to Fox,146 the vastus medialis is the weakest of the quadriceps group and appears to be the first muscle of the quadriceps group to atrophy and the last to rehabilitate.147 The normal VMO/VL ratio of electromyographic (EMG) activity in standing knee extension from 30 to 0 degrees is 1:1,148 but in patients who have patellofemoral pain, the activity in the VMO decreases significantly; instead of being tonically active, it becomes phasic in action.149 The presence of swelling also inhibits the VMO, and it requires almost half of the volume of effusion to inhibit the VMO as it does to inhibit the rectus femoris and VL muscles.150

The VMO is frequently innervated independently from the rest of the quadriceps by a separate branch from the femoral nerve.137

Vastus Medialis Longus

The VML originates from the medial aspect of the upper femur and inserts anteriorly into the quadriceps tendon, giving it a line of action of approximately 15–17 degrees off the long axis of the femur in the frontal plane.138

Since the quadriceps group is aligned anatomically with the shaft of the femur and not with the mechanical axis of the lower extremity, any quadriceps muscle contraction (regardless of knee flexion angle) results in compressive forces acting on the patellofemoral joint.151

Hamstrings

As a group, the hamstrings primarily function to extend the hip and to flex the knee. The hamstrings are innervated by branches of the sciatic nerve.

Semimembranosus Muscle

The semimembranosus muscle (Fig. 19-8) arises from the lateral facet of the ischial tuberosity and the ischial ramus. This muscle inserts into the posteromedial aspect of the medial tibial condyle and has an key expansion that reinforces the posteromedial corner of the knee capsule. The semimembranosus pulls the meniscus posteriorly, and internally rotates the tibia on the femur, during knee flexion, although its primary function is to extend the hip and flex the knee.

Semitendinosus Muscle

The semitendinosus muscle (see Fig. 19-8) arises from the upper portion of the ischial tuberosity via a shared tendon with the long head of the biceps femoris. From there, it travels distally, becoming cord-like about two-thirds of the way down the posteromedial thigh. Passing over the MCL, it inserts into the medial surface of the tibia and deep fascia of the lower leg, distal to the gracilis attachment, and posterior to the sartorius attachment. These three structures are collectively called the pes anserinus (“goose foot”) at this point. Like the semimembranosus, the semitendinosus functions to extend the hip, flex the knee, and internally rotate the tibia.

Biceps Femoris

The biceps femoris (see Fig. 19-8) muscle is a two-headed muscle. The longer of the two heads arises from the inferomedial facet of the ischial tuberosity, whereas the shorter head originates from the lateral lip of the linea aspera of the femur. The muscle inserts on the lateral tibial condyle and the fibular head. The biceps femoris functions to extend the hip, flex the knee, and externally rotate the tibia. The superficial layer of the common tendon has been identified as the main force creating external tibial rotation and controlling internal rotation of the femur.152 The pull of the biceps on the tibia retracts the joint capsule and pulls the iliotibial tract posteriorly, keeping it tight throughout flexion.

Gastrocnemius

The gastrocnemius originates from above the knee by two heads, each head connected to a femoral condyle and to the joint capsule (Fig. 20-4). Approximately halfway down the leg, the gastrocnemius muscles merge to form an aponeurosis. As the aponeurosis gradually contracts, it accepts the tendon of the soleus, a flat broad muscle deep to the gastrocnemius. The aponeurosis and the soleus tendon end in a flat tendon, called the Achilles tendon, which attaches to the posterior aspect of the calcaneus. The two heads of the gastrocnemius and the soleus are collectively known as the triceps surae (see Chap. 21).

Although the primary function of the gastrocnemius–soleus complex is to plantar flex the ankle and to supinate the subtalar joint, the gastrocnemius also functions to flex or extend the knee, depending on whether the lower extremity is weight-bearing or not. It has been proposed that weakness of the gastrocnemius may cause knee hyperextension.153

In addition, it has been theorized that the gastrocnemius acts as an antagonist to the ACL, exerting an anteriorly directed pull on the tibia throughout the range of knee flexion–extension motion, particularly when the knee is near extension.154,155

Popliteus

The popliteus originates from the lateral femoral condyle near the LCL. The muscle has several attachments, including the lateral aspect of the lateral femoral condyle, the posterior-medial aspect of the head of the fibula and the posterior horn of the lateral meniscus.156 The larger base of this triangular muscle inserts obliquely into the posterosuperior part of the tibia above the soleal line. The muscle has several important functions, including the reinforcement of the posterior third of the lateral capsular ligament67 and the unlocking of the knee during flexion from terminal knee extension. It performs this latter task by internally rotating the tibia on the femur (a good example of an arcuvial muscle), preventing impingement of the posterior horn of the lateral meniscus by drawing it posteriorly, and, with the PCL, preventing a posterior glide of the tibia.67,157–159 Since knee joint injury frequently involves some component of transverse-plane rotation and the popliteus muscle has been described as an important, primary, dynamic, transverse-plane, rotatory knee joint stabilizer, an understanding of its function in relation to other posterolateral knee joint structures is important.160 Attached to the popliteus tendon is the popliteofibular ligament, which forms a strong attachment between the popliteal tendon and the fibula. This ligament adds to posterolateral stability.161–164 A medial portion of the popliteus penetrates the joint, becoming intracapsular with the lateral meniscus. This part of the popliteus tendon is pain sensitive, and an injury here can often mimic a meniscal injury on the lateral aspect of the joint line.73 Differentiation between these two lesions can be elucidated with the reproduction of pain with resisted flexion in an extended and externally rotated position of the tibia if the popliteus is involved.

Hip Adductors

The hip adductors, which play an indirect role in the medial stability of the knee (Table 20-3), are described in Chapter 19. The exception to this is the two-joint gracilis muscle, the third member of the pes anserinus group, which in addition to adducting and flexing the hip, assists in flexion of the knee and internal rotation of the lower leg.

Tensor Fascia Latae

The tensor fascia latae (TFL) arises from the outer lip of the iliac crest and the lateral surface of the anterior superior iliac spine (ASIS) (Fig. 19-5). Over the flattened lateral surface of the thigh, the fascia latae thickens to form a strong band, the iliotibial tract.16 When the hip is flexed, the TFL is anterior to the greater trochanter and helps maintain the hip in flexion. As the hip extends, the TFL moves posteriorly over the greater trochanter to assist with hip extension. The TFL is also a weak extensor of the knee, but only when the knee is already extended. The muscle is innervated by the superior gluteal nerve, L4–L5.

Iliotibial Band (Tract)

The ITB or tract begins as a wide covering of the superior and lateral aspects of the pelvis and thigh in continuity with the fascia latae (Fig. 20-4 and Fig. 19-5). It inserts distal and lateral to the patella at the tubercle of Gerdy on the lateral condyle of the tibia. Anteriorly, it attaches to the lateral border of the patellar. Posteriorly, it is attached to the tendon of the biceps femoris. Laterally, it blends with an aponeurotic expansion from the VL165 (see Chap. 19).

Like the patella tendon, the ITB can be viewed as a ligament or a tendon. Its location adjacent to the center of rotation of the knee allows it to function as an anterolateral stabilizer of the knee in the frontal plane166 and to both flex and extend the knee.138,167 During stationary standing, the primary function of the ITB is to maintain knee and hip extension, providing the thigh muscles an opportunity to rest. While walking or running, the ITB helps maintain flexion of the hip and is a major support of the knee in squatting from full extension until 30 degrees of flexion. In knee flexion greater than 30 degrees, the iliotibial tract becomes a weak knee flexor, as well as an external rotator of the tibia.

The posterior structure of the knee joint is a complex of nerves and blood vessels. The major blood supply to this area comes from the femoral, popliteal, and genicular arteries.16

Femoral Nerve

The course and distribution of the femoral nerve is described in Chapter 3.

Saphenous Nerve

The saphenous nerve is the largest cutaneous branch of the femoral nerve (L2–L4). It leaves the subsartorial canal approximately 8–10 cm above the medial condyle of the knee and gives off branches to the medial aspect of the knee. Entrapment of the saphenous nerve during its course here can occur because of direct trauma, genu valgus, or knee instability, resulting in saphenous neuritis.

Sciatic Nerve

The sciatic nerve (see Chap. 3) provides motor branches to the hamstrings and all muscles below the knee.168 It also provides the sensory innervation to the posterior thigh and entire leg and foot below the knee (except the medial aspect, which is innervated by the saphenous nerve).168 The tibial and fibular (peroneal) divisions of the sciatic nerve serve the posterior aspect of the knee. The common fibular (peroneal) nerve is formed by the upper four posterior divisions (L4, L5, and S1, S2) of the sacral plexus, and the tibial nerve, is formed from all five anterior divisions (L4, L5, and S1–S3).

Common Fibular (Peroneal) Nerve

The common fibular (peroneal) nerve is a component of the sciatic nerve as far as the upper part of the popliteal space. At the apex of the popliteal fossa, the common fibular (peroneal) nerve begins its independent course, descending along the posterior border of the biceps femoris, before traveling diagonally across the posterior aspect of the knee joint to the upper external portion of the leg near the head of the fibula.16 Sensory branches are given off in the popliteal space. These include the superior and inferior articular branches to the knee joint, and the lateral sural cutaneous nerve.16 The latter nerve joins the medial calcaneal nerve (from the tibial nerve) to form the sural nerve, supplying the skin of the lower posterior aspect of the leg, the external malleolus, and the lateral side of the foot and fifth toe.16

The common fibular (peroneal) nerve curves around the lateral aspect of the fibula toward the anterior aspect of the bone, before passing deep to the two heads of the fibularis (peroneus) longus muscle, where it divides into three terminal branches: the recurrent articular, and the superficial and deep fibular (peroneal) nerves. The recurrent articular nerve accompanies the anterior tibial recurrent artery, supplying branches to the proximal tibiofibular and knee joints, and a twig to the tibialis anterior muscle.

Tibial Nerve

The tibial nerve, the larger of the two branches of the sciatic nerve, begins its own course in the upper part of the popliteal space. It descends vertically through this space, passing between the heads of the gastrocnemius muscle to the posterior aspect of the leg, and to the posteromedial aspect of the ankle, where its terminal branches serve the foot and ankle (see Chap. 21).

The tibial nerve supplies the gastrocnemius, plantaris, soleus, popliteus, tibialis posterior, flexor digitorum longus pedis, and flexor hallucis longus muscles. Articular branches pass to the knee and ankle joints.

Tibiofemoral Joint

The tibiofemoral joint, or knee joint, is a ginglymoid, or modified hinge joint, which has six degrees of freedom. The bony configuration of the knee joint complex is geometrically inappropriate and lends little inherent stability to the joint. Joint stability is therefore reliant on the static restraints of the joint capsule, ligaments, and menisci, and the dynamic restraints of the quadriceps, hamstrings, and gastrocnemius.36,169 Since the ligaments share tensile load-carrying functions with the musculotendinous units, these structures can be considered to complement each other's functions directly.36 The PCL is located very near the long axis of tibial rotation and has been described as the main stabilizer of the knee.170

The motions that occur about the knee consist of flexion and extension, coupled with other motions such as varus and valgus motions, and external and internal rotation. This is because the longitudinal axis of the knee is not perpendicular to the sagittal plane, but lies along a line that connects the origins of the collateral ligaments on the medial and lateral femoral epicondyles.12,171

All the motions about the tibiofemoral joint consist of a rolling, gliding, and rotation between the femoral condyles and the tibial plateaus (Fig. 20-5). This rolling, gliding, and rotation occurs almost simultaneously, albeit in different directions, and serves to maintain joint congruency.5,172

• Flexion and extension occur with a mediolateral translation around a mediolateral axis. In the relaxed standing position, with the knee straight or slightly flexed, the vector force is behind the knee; therefore there is a tendency for further knee flexion unless the quadriceps contracts.110
• A varus–valgus angulation occurs with anteroposterior translation around an anteroposterior axis.
• External and internal rotation of the joint occurs with superior–inferior translation around a superoinferior axis and transverse plane. The available range of motion (ROM) in rotation is dependent on the flexion–extension position of the knee.173 The amount of rotation progressively increases from no rotation at terminal extension to 70 degrees of rotation (40 degrees of external rotation and 30 degrees of internal rotation) available at 90 degrees of flexion. The amount of available rotation decreases as further flexion occurs.5,111

During the initial 30 degrees of knee flexion, the LCL provides a greater contribution to resisting tibial varus and the PMTC provides a greater contribution to resisting tibial external rotation and posterior translation.160,174 For flexion to be initiated from a position of full extension, the knee joint must first be “unlocked.” As mentioned previously, the service of locksmith is provided by the popliteus muscle, which acts to internally rotate the tibia with respect to the femur, enabling flexion to occur.97

During flexion of the knee, the femur rolls posteriorly and glides anteriorly, with the opposite motion occurring during extension of the knee. This arrangement resembles a twin wheel, rolling on a central rail. Available knee flexion can vary between 120 and 160 degrees, depending on the position of the hip and the girth of the soft tissues around the leg and the thigh.

From 30–5 degrees of weight-bearing knee extension (moving toward full knee extension), the lateral condyle of the femur, together with the lateral meniscus, become congruent, moving the axis of movement more laterally. The tibial glide now becomes much greater on the medial side, which produces internal rotation of the femur, and the ligaments, both extrinsic and intrinsic, start to tighten near terminal extension. At this point, the cruciates become crossed and are tightened.

In the last 5 degrees of extension, rotation is the only movement accompanying extension. This rotation is referred to as the “screw home” mechanism and is a characteristic motion in the normal knee, in which the tibia externally rotates and the femur internally rotates as the knee approaches extension (Fig. 20-3). This motion is known to be a complex function of surface geometry, tension in the ligamentous structures, and the action of muscles,175,176 and has been described both in vivo177–180 and in vitro.181,182

Knee hyperextension is usually available from 0 to 15 degrees.183 During knee hyperextension, the femur does not continue to roll anteriorly but instead tilts forward. This creates anterior compression between the femur and the tibia.153 In the normal knee, bony contact does not limit hyperextension as it does at the elbow. Rather, hyperextension is checked by the soft tissue structures. When the knee hyperextends, the axis of the thigh runs obliquely inferiorly and posteriorly, which tends to place the ground reaction force anterior to the knee. In this position, the posterior structures are placed under tension, which helps to stabilize the knee joint, negating the need for quadriceps muscle activity.157

The normal capsular pattern of the knee joint is gross limitation of flexion and slight limitation of extension. The ratio of flexion to extension is roughly 1:10; thus, 5 degrees of limited extension corresponds to a 45–60-degree limitation of flexion. The causes of a capsular pattern in the knee are the same as for any other joint. These include traumatic arthritis, rheumatoid and reactive arthritis, osteoarthrosis, monarticular and steroid-sensitive arthritis, crystal synovitis or gout, hemarthrosis, and septic arthritis.

Open-kinetic chain (OKC) and closed-kinetic chain (CKC) exercises have different effects on tibial translation and ligamentous strain and load:

• During active OKC knee extension, the shear component produced by unopposed contraction of the quadriceps depends on the angle of knee flexion, increasing as the knee flexion angle increases.
• During CKC exercises for the lower extremity, the flexion moment arms of the knee and hip increase as a squat is performed.

Patellofemoral Joint

The patella is an inactive component of the knee extensor mechanism, in which the static and dynamic interactions of the underlying tibia and femur determine the patellar-tracking pattern. As the knee flexes, the compression forces between the patella and the femur increase (see “Patellofemoral Joint Reaction Force” section) as the contact surface area increases, in an attempt to normalize the contact stress unit load. Even though the surface area increases with knee flexion, it cannot keep up with these increased joint reaction forces. To assist in the control of the forces around the patellofemoral joint, there are a number of static and dynamic restraints. The static restraints include the following:

• Medial retinaculum. Although not as robust as its lateral counterpart, the medial retinaculum is the primary static restraint to lateral patellar displacement at 20 degrees of knee flexion, contributing 60% of the total restraining force.185
• Bony configuration of the trochlea. The patellofemoral joint is intrinsically unstable because the tibial tubercle lies lateral to the long axis of the femur and the quadriceps muscle and the patella is therefore subject to a laterally directed force.186 If the patella fails to engage securely in the patellar groove at the start of flexion, it slips laterally, and as flexion continues, it can dislocate completely or slip back medially to its correct position.186 The causes of insufficient engagement include
  • an abnormally high patella,
  • patellar dysplasia,
  • a poorly developed patellar groove (trochlea).
• Medial patellomeniscal ligament and lateral retinaculum. These structures contribute 13% and 10% of the restraint to translation of the patella, respectively.
• Passive restraints. The passive restraints to translation of the patella are provided by the structures that form the superficial and deep lateral retinaculum.

The primary dynamic restraints to patellar motion are the quadriceps muscles, particularly the VMO. The activity of the VMO increases as the torque around the knee increases, and it provides the only dynamic medial stability for the patella.145,150 However, the muscle vector of the VMO is more vertical than normal when a patellar malalignment is present, making it less effective as a dynamic stabilizer.187,188 The timing of the VMO contractions relative to those of other muscles, especially the VL, also appears to be critical and has been found to be abnormal with patellar malalignment.137,189–192

Deficits in the timing of muscle activity have been identified in other musculoskeletal conditions such as lower back pain, in which the EMG activity of transversus abdominus has been shown to be delayed compared with a control group191,193 (see Chap. 28).

A study by Cowan et al.,191 which found that on average the onset of EMG activity of the VL occurred before that of VMO in subjects with patellofemoral pain syndrome, appears to lend support to this theory. Thus, specific retraining of the VMO is believed to improve patellar tracking.191

The quadriceps (Q) angle can be described as the angle formed by the bisection of two lines, one line drawn from the ASIS to the center of the patella, and the other line drawn from the center of the patella to the tibial tubercle194 (Fig. 20-6). The angle is a measure of the tendency of the patella to move laterally when the quadriceps muscles are contracted.195,196

The Q-angle was originally described by Brattström,197 although many authors had previously described the importance of genu valgus and its relationship to patellofemoral instability. Brattström described the Q-angle as the angle formed by the resultant vector of the quadriceps force and the patellar tendon with the knee in an “extended, end-rotated” position.

Various normal values for the Q-angle have been reported.126,194,198–201 The most frequent ranges cited are 8–14 degrees for males and 15–17 degrees for females. The discrepancy between males and females allegedly results from the wider pelvis of the female, although this has yet to be proven. Indeed, it is not even clear that, on average, women have a significantly greater Q-angle.199,202 Angles of greater than 20 degrees are considered abnormal and may be indicative of potential displacement of the patella.203–205

The Q-angle can vary significantly with the degree of foot pronation and supination, and when compared with measurements made in the supine position.201,206 Confusing this issue is that the Q-angle is increased in patients with a lateralized tibial tuberosity, but it can be falsely normal when the patella is laterally displaced.11

The significance of a normal Q-angle was highlighted in a study by Huberti and Hayes207 who concluded that, with a normal physiologic Q-angle, the pressure distributions on the patella were remarkably uniform at each of the angles of knee flexion tested (20, 30, 60, 90, and 120 degrees) between the medial and lateral facets. In contrast, when the physiologic Q-angle was decreased by 10 degrees, the patellar contact pressure increased by 53% at 20 degrees of knee flexion. However, when the knee flexion angle increased beyond 20 degrees, the contact pressure actually decreased, with the lowest value at 90 degrees.207

Although this measurement has been used to evaluate and treat patellofemoral joint pathology, few studies have examined its reliability. Greene et al.208 evaluated the interobserver and intraobserver reliability of the Q-angle measurement comparing clinically derived Q-angle measurements with radiographically derived measurements. A reliability analysis was performed using intraclass correlation coefficients (ICCs). For interobserver measurements, the ICCs ranged from 0.17 to 0.29 for the four variables evaluated (right and left, extension and flexion). For intraobserver measurements, the ICCs ranged from 0.14 to 0.37. The average ICC between the clinically and radiographically derived measurements ranged from 0.13 to 0.32, which demonstrates poor interobserver and intraobserver reliability of Q-angle measurement and poor correlation between clinically and radiographically derived Q-angles.

The A angle is another measurement that has been used to evaluate and treat patellofemoral joint pathology and as a quantitative measurement of patellar realignment. The A angle is defined as the relationship between the longitudinal axis of the patellar and the patella tendon, or the patella's orientation to the tibial tubercle. The angle is created by drawing imaginary lines through the patella longitudinally and from the tibial tuberosity to the apex of the inferior pole of the patella. An A angle greater than 35 degrees is often cited as a cause of patellar pathomechanics. Ehrat et al.210 performed a study to determine intrarater and interrater reliability for the A angle. The results of the study indicated that the A angle was not reproducible and further study is needed before the A angle can be used as a reliable assessment tool for patellar position.

Patella–Femur Contact and Loading

In view of the frequent problems associated with the patellofemoral joint, it is remarkable that, for much of the time, the articulating surfaces of this joint are not even in contact.211 Indeed, there is no bone-to-bone contact with the femur in full knee extension, or during standing or walking on level ground11,212,213 (Table 20-4).

The amount of contact between the patella and the femur appears to vary according to a number of factors, including (1) the angle of knee flexion, (2) the location of contact, (3) the surface area of contact, and (4) the patellofemoral joint reaction force (PJRF).211 Each of these factors is discussed separately.

Angle of Knee Flexion

As knee flexion proceeds, the quadriceps vector becomes more perpendicular, and the force on the patella gradually increases (Fig. 20-7).214 This increasing force is somewhat dissipated by the increased patellofemoral contact with increasing flexion (see later discussion).147 However, because the force increases more rapidly than the surface area, the stress on the patella increases significantly with flexion.212 Any muscle imbalance between the lateral and medial quadriceps muscles can affect the patellar alignment and distribution of pressure in the lower flexion angles of less than 60 degrees.211 This can produce a rotation of the patella in the coronal plane.215 At higher flexion angles, imbalances are likely to produce a tilt of the patella in the sagittal plane.215

Location of Contact

In the normal knee, as the knee flexes from 10 to 90 degrees, the contact area shifts gradually from the distal to the proximal pole of the patella.207,213,216,217 At full extension, the patella is not in contact with the femur, but rests on the supratrochlear fat pad.215 From full extension to 10 degrees of flexion, the tibia internally rotates, allowing the patella to move into the trochlea.211 This brings the distal third of the patellar into contact with the femur. From 10 to 20 degrees of flexion, the patella contacts the lateral surface of the femur on the inferior patellar surface.213,218 The middle surfaces of the inferior aspect of the patellar come into contact with the femur at around 30–60 degrees of flexion, at which point the patella is well seated in the groove.213,218 As the knee continues to flex to 90 degrees, the patella moves laterally, and the area of patella contact moves proximally.211 At 90 degrees of knee flexion, the entire articular surface of the patella (except the odd facet) is in contact with the femur.213,218 Beyond 90 degrees, the patella rides down into the intercondylar notch. At this point, the medial and lateral surfaces of the patella are in contact with the femur, and the quadriceps tendon articulates with the patellar groove of the femur.211 At approximately 120 degrees of knee flexion, there is no contact between the patella and the medial femoral condyle.188,219 At 135 degrees of knee flexion, the odd facet of the patella makes contact with the medial femoral condyle.213,218

Surface Area of Contact

Knowledge of the patellofemoral contact pattern is useful for determining the limits of motion when patients with patellofemoral symptoms perform OKC and CKC exercises. 216 Some authors have proposed that the contact area quadruples as the knee flexes from 20 to 90 degrees.86,192

Patellofemoral Joint Reaction Force

The PJRF is a function of quadriceps and patellar tendon tension and of the angle formed between the quadriceps and patellar tendon. These forces are caused by the increase in patellar and quadriceps tendon tension and the increase in the acuity of the Q-angle that occurs during knee flexion.192,217,220,221

OKC and CKC exercises produce different effects on PJRF and contact stress per unit area:

• During OKC extension, the flexion moment arm for the knee increases as the knee extends from 90 degrees of flexion to full extension (0 degree), resulting in increased quadriceps and patellar tendon tension and increasing PJRFs. Clinicians most often allow OKC exercises at 90–40 degrees of knee flexion as this range provides the lowest PJRF while producing the greatest amount of patellofemoral contact area.
• During CKC exercises, the flexion moment arm of the knee increases as the angle of knee flexion increases (Fig. 20-7). Maximum force in the quadriceps muscle and patellar tendon is generated at 60 degrees of flexion with values approaching 3000 N.217 CKC, such as the leg press and wall squat, are typically prescribed initially at 0–16 degrees and then progressed to 0–30 degrees where the PJRFs are lower.

Patellar Stability

Once engaged, the patella is held in place as flexion proceeds by two mechanisms:

1. Static restraints. The primary static restraints for this joint are the medial and lateral retinacula and the contact of the patella with the lateral edge of the patellar groove.

•     a. Appropriate tension within the retinacula assures patellar tracking through the groove. Inappropriate tensioning may result in excessive pressure on the lateral patellofemoral joint surfaces (lateral patellofemoral pressure syndrome) or medial subluxation of the patella from the groove.
•     b. The trochlea acts as a lateral buffer to the patella. Sometimes the patella engages correctly at the start of the flexion but subluxes or dislocates as flexion proceeds.186 This disengagement may be the result of a defective lateral trochlear margin, an unusually shallow groove, or malalignment (if excessive genu valgus is present, the laterally directed force applied to the patella is greater).

2. Dynamic restraints. The dynamic restraints of the patellofemoral joint are the quadriceps muscle and the extensor mechanism in general. The tension provided by these soft tissues can prevent the patella from slipping laterally. However, excessively tight lateral structures or deficient medial structures may increase the laterally directed force. This may result in maltracking of the patella or possible subluxation.146 The lateral structures (VL, lateral retinaculum, and iliotibial band) may be tight from fibrosis of the VL222 or adaptively shortened for no obvious reason.186 The medial structures (medial retinaculum) may be loose after injury to the medial retinaculum, from stretching after repeated dislocations, or from severe wasting of the vastus medialis.186

Patellar Tracking

Patellar tracking, specifically patella maltracking, continues to be the subject of much study.188,192,223–225 In the normal knee, the patella glides in a sinuous path inferiorly and superiorly during flexion and extension, respectively, covering a distance of 5–7 cm with respect to the femur.226 A concave, lateral, C-shaped curve is produced by the patella as it moves from approximately 120 degrees of knee flexion toward approximately 30 degrees of knee extension. The lateral curve produces a gradual medial glide of the patella from 45 to 15 degrees of knee flexion in the frontal plane and a medial tilt (from 45 to 0 degrees of knee extension) in the sagittal plane.192,224 Further extension of the knee (between 15 and 0 degrees) produces a lateral glide of the patella in the frontal plane and a lateral tilt in the sagittal plane.192,224

One proposed mechanism for abnormal patellar tracking is an imbalance in the activity or tension of the medial and lateral restraints.190,191,227

The cause of the imbalance tends to be hypertonus of the VL, or an excessively tight TFL or ITB.211 Other joints within the lower kinetic chain can also influence the tracking of the patella.

As previously discussed, in relation to the lower kinetic chain, which includes the lumbar spine, pelvic joints, hip, knee, foot, and ankle joints, the motions that occur during activities can be described as CKC or OKC motions.

Since the knee joint complex is an integral part of the lower kinetic chain, movement at any portion of the kinetic chain will influence knee joint mechanics, necessitating an examination of the entire chain as part of a comprehensive assessment. Kinetic chain exercises need to be monitored carefully to detect the influence of any abnormal motion that occurs in one portion of the segment on the remaining portions of the kinetic chain.228 For example, normal biomechanics dictate that the tibiofemoral joint extends during midstance as the body traverses the fixed foot. Excessive pronation in either magnitude or duration prevents the knee joint from acquiring the necessary external rotation of the tibia for this extension, which in turn may affect patella tracking.150,229

Another example occurs during the descending phase of a squat, which requires simultaneous flexion at the hip and knee, and dorsiflexion at the ankle. If ankle dorsiflexion motion is limited, subtalar joint pronation will increase to compensate for the lack of dorsiflexion.228,229 This increased pronation, which is coupled with internal rotation of the lower extremity, results in an increase in the functional Q angle and may contribute to persistent patellofemoral pain.228

Whether the motion occurring at the knee joint complex occurs as a CKC or OKC has implications on the biomechanics and the joint compressive forces induced. A significant number of studies42,230–242 have examined the biomechanics of the knee during OKC and CKC activities and have attempted to quantify and compare cruciate ligament tensile forces, tibiofemoral compressive forces, and muscle activity about the knee during these activities.

Closed-Kinetic Chain Motion

Tibiofemoral Joint

During CKC knee flexion, the femoral condyles roll backward and glide forward on the tibia. During CKC knee extension, the femoral condyles roll forward and slide backward. During CKC knee flexion, as the femur rolls posteriorly, the distance between the tibial and femoral insertions of the ACL increases. Since the ACL cannot lengthen, it guides the femoral condyles anteriorly.183 In contrast, during CKC extension of the knee, the distance between the femoral and tibial insertions of the PCL increases. Since the PCL cannot lengthen, the ligament pulls the femoral condyles posteriorly as the knee extends.183

It has been suggested by some studies that the CKCE, with its axial loading of the joint, and resultant joint compressive forces and minimization of shear forces exerted across the knee, may protect the anterior cruciate-graft during quadriceps exercises through use of the contours of the joint, thereby providing greater stabilization to the knee. 243,244 Other studies have shown that CKCEs such as squatting do not necessarily protect the ACL any more than OKC flexion and extension exercises245 (see Table 20-4). However, increasing the resistance during the CKCEs does not produce a significant increase in ACL strain values, unlike increasing the resistance during OKC flexion–extension exercises.245

It would appear that CKCEs are only beneficial if performed in a restricted range, with some studies demonstrating that CKCEs at greater than 30 degrees of knee flexion can exacerbate patellofemoral problems.232,234

Thus, a “paradox of exercise”233 is encountered for the patient recovering after an ACL reconstruction, whereby the patient risks excessive ACL strain if these exercises are performed at less than 30 degrees of knee flexion, but patellofemoral joint complications if the exercises are performed at greater than 30 degrees of knee flexion.235 Consequently, patients undergoing ACL rehabilitation who are susceptible to patellofemoral pain should be forewarned about potential patellofemoral joint complications when performing these exercises. These patients should also be advised to inform the clinician of any anterior knee pain that develops during their rehabilitative process.

Patellofemoral Joint

During CKCEs, the flexion moment of the arm increases as the angle of knee flexion increases. In addition, the joint-reaction force increases proportionately more during knee flexion than the magnitude of the contact area.188 Thus, the articular pressure gradually increases as the knee flexes from 0 to 90 degrees,188 with maximum values occurring at 90 degrees of flexion.207 However, because this increasing force is distributed over a larger patellofemoral contact area, the contact stress per unit area is minimized. Changes in the Q-angle of 10 degrees can increase patellofemoral contact pressures by 45% at 20 degrees of flexion.207 As the Q-angle increases, the patella tends to track more laterally.147 A 50% decrease in tension in the VMO can displace the patella laterally by up to 5 mm.215

From 90 to 120 degrees of flexion, the articular pressure remains essentially unchanged because the quadriceps tendon is in contact with the trochlea, which effectively increases the contact area.246

Thus, for the patellofemoral joint, CKCEs are performed in the 0–45-degree range of flexion, with caution used when exercising between 90 and 50 degrees of knee flexion, where the PJRFs can be significantly greater.246

Open-Chain Motion

Tibiofemoral Joint

During OKC flexion, the tibia rolls and glides posteriorly on the femur, while during extension the opposite occurs. OKC knee extension involves a conjunct external rotation of the tibia, while OKC knee flexion involves a conjunct internal rotation of the tibia.

OKC activities produce shear forces at the tibiofemoral joint in the direction of tibial movement. For example, OKC knee extension produces anterior shear stresses.247 As the ACL provides 85% of the restraining force to this tibial shear,39 OKC knee extension may compromise a repaired or reconstructed ACL,248 especially in the last 45 degrees of knee extension,247,249,250 although at full extension, the ACL is under no tension.26,231,248,251–253 However, if resistance is applied to the lower leg during OKCEs, an increase in strain on the ACL is demonstrated,26 particularly in the last few degrees of extension.36 OKCE is preferred over CKCE if minimal PCL tensile force is desired. Since PCL tension generally increases with knee flexion, knee ROMs that are less than 60 degrees will minimize PCL tensile force.235 The higher compressive forces that occur during the beginning and end ranges of knee flexion in OKCE may serve to unload some of the tensile force in these respective cruciate ligaments.235

Both OKCEs and CKCEs appear equally effective in minimizing ACL tensile force, except during the final 25 degrees of knee extension in OKCEs.

OKC flexion, resulting from an isolated contraction of the hamstrings, reduces ACL strain throughout the ROM,26 but increases the strain on the PCL as flexion increases from 30 to 90 degrees.251

Patellofemoral Joint

In an OKC activity, the forces across the patella are their lowest at 90 degrees of flexion. As the knee extends from this position, the flexion moment arm (contact stress/unit) for the knee increases, peaking between 35 and 40 degrees of flexion, while the patella contact area decreases.232,254 This produces an increase in the PJRF at a point when the contact area is very small. At 0 degrees of flexion (full knee extension), the quadriceps force is high, but the contact stress/unit is low.

Thus OKCEs for the patellofemoral joint should be performed from 25 to 90 degrees of flexion (60–90 degrees if there are distal patellar lesions), or at 0 degree of extension (or hyperextension) from a point of view of cartilage stress.246 OKCEs are not recommended for the patellofemoral joint between 0 and 45 degrees of knee flexion, especially if there are proximal patellar lesions, as the PJRFs are significantly greater.246

The common pathologies for the knee joint complex are detailed after this section. An understanding of both is obviously necessary. Since mention of the various pathologies occurs with reference to the examination, and vice versa, the reader is encouraged to switch between the two discussions.

History

With the vast number of specific tests available for the knee joint complex, it is tempting to overlook the important role of the history, which can detail both the chronology and mechanism of events. The diagnosis of most tibiofemoral and patellofemoral joint disorders often can be made on the basis of a thorough history and physical examination alone. The patient's family history, medical history, and history of the present knee problem are necessary for a complete diagnosis. A medical screening questionnaire for the knee, leg, ankle, and foot region is provided in Table 20-5. In addition to those questions outlined in “History” section in Chapter 4, the clinician should determine the following:

Chief Complaint

It is important to elucidate the exact nature and location of the patient's chief complaint. Does the complaint relate to pain or instability, or both? If the chief complaint is pain, is there a history of recent trauma?

Onset of Symptoms

Questions about the onset of symptoms (traumatic versus insidious) are, as with any joint, important. Acute injuries are often traumatic and can be associated with both pain and instability. Reports of immediate pain associated with an inability to weight bear can indicate a muscle, ligament, or fracture injury and should be related to the patient's current complaints to identify the likely cause. As always, an insidious onset of pain should alert the clinician to the possibility of a serious condition. Pain in the knee can be referred from the hip, the back, and the sacroiliac joint. Complaints of shooting pain, burning pain, and pain that travels down the thigh should be carefully investigated using a lumbar screen to rule out radicular symptom production. A gradual, nontraumatic onset of knee pain could also indicate patellofemoral joint dysfunction or symptomatic degenerative joint disease of the knee joint complex. The characteristic clinical features in an uncomplicated osteoarthritis (OA) of the knee joint are a dull and aching pain that occurs at the end of the day or after prolonged periods of standing or walking.255 As the disease progresses, there is pain and stiffness on rising in the morning, which eases with activity or rest, and a limitation of movement in the capsular pattern.

Mechanism of Injury

The clinician should determine how exactly the injury happened—was it a traumatic blow, a contact injury, a noncontact injury, or did the patient fall? The position of the joint at the time of the traumatic force dictates which anatomic structures are at risk for injury; hence, an important aspect of obtaining the patient's history for acute injuries is to allow him or her to describe the position of the knee and direction of forces at the time it was injured.256 The direction the patient was turning to and the direction of the blow help to determine the structures likely affected.257 Twisting injuries can result in injuries to the ligaments or meniscus. Contact injuries can result in deep bone bruising, muscle contusions, and ligamentous or meniscal injury when combined with twisting or hyperextension.

The primary mechanisms of injury in the knee are direct trauma, a varus or valgus force (with or without rotation), hyperextension, flexion with posterior translation, a twisting force, and overuse.258

• Direct trauma. A direct blow to the anterior aspect of the knee may cause a patellar injury. Repetitive microtrauma to the patella may also be a factor. For example, Bloom259 describes a condition called airplane knee, in which the frequent flyer in coach class gets repetitive knee bumps from the passenger in front when the seat is dropped back suddenly.
• Valgus force. A history of a valgus force to the knee without rotation could indicate damage to the medial meniscus, collateral ligament, epiphyseal plate, or patellar dislocation–subluxation.256 A history of a valgus force with rotation could indicate damage to the ACL, or the posteromedial capsule (the so-called unholy triad).
• Varus force. A history of a varus force with rotation can involve the LCL, the posterolateral capsule, and the PCL.256
• Hyperextension. A hyperextension force can result in ACL injuries and associated medial meniscal tears. Complaints of buckling or giving way after the injury can reinforce a suspicion of ligamentous involvement.
• Flexion. During flexion, as the tibia internally rotates, the posterior horn of the medial meniscus is pulled toward the center of the joint. If excessive, this movement can produce a traction injury of the medial meniscus, tearing it from its peripheral attachment and producing a longitudinal tear of the substance of the meniscus.257
• Flexion with a posterior translation. This mechanism can result in a PCL injury.
• Twisting force. Meniscal injuries are usually associated with a torsional force that combines compression and rotation, often in activities that require cutting maneuvers.259 In addition, the ACL often is injured during traumatic twisting injuries in which the tibia moves forward with respect to the femur, often accompanied by valgus stress.257 No direct blow to the knee or leg is required, but the foot is usually planted and the patient may remember a “popping” sensation at the time of the injury. Similar to the ACL, PCL injuries often occur during twisting with a planted foot in which the force of the injury is directed posteriorly against the tibia with the knee flexed.257
• Overuse. Patellar injury is most often a result of overuse.259 Typically, there is an associated 4–6-week training program change. These changes can include (1) increasing a training load more than 10% per week; (2) not allowing a 15% decrease for a week off; (3) not using an alternate-day or hard-easy pattern; (4) changing quickly from flat to hill training; (5) running in one direction on a canted road; (6) running in worn-out shoes; or (7) biking in cleated shoes that fix the tibial rotation relative to the pedal.259

Location of Symptoms

The location of the symptoms may afford the clinician clues as to the cause. Initially, the clinician should consider the anatomical structures underlying the area of pain to ascertain the cause. Medial knee pain can be caused by a spectrum of possibilities ranging from localized musculoskeletal to nonmusculoskeletal pathology (Table 20-6).260 For example, medial meniscal lesions frequently result in posterior medial joint line pain and mild medial joint line pain.256 Medial knee pain also may suggest an MCL injury. MCL injury can produce pain at the medial femoral condyle, medial joint line, or proximal tibia.256 Lateral joint line pain may be caused by an LCL injury. Localized swelling over specific knee structures, such as the MCL or LCL, also may accompany the pain. Midlateral joint line pain often is caused by a lateral meniscal lesion. Patellofemoral joint pain usually is anterior, radiating medially and laterally, but primarily in, around, or under the patella.259 Posterior knee pain may be secondary to joint effusion producing distention of the posterior capsule, a mild strain of one of the gastrocnemius muscles or a PCL tear.256 Posterior knee pain accompanied by snapping could indicate a Baker's cyst.

Behavior of Symptoms

Symptoms that are not alleviated with rest could indicate a nonmechanical source, or a chemically induced source, such as an inflammatory reaction. A hot and swollen joint without a history of trauma should provoke suspicions about hemophilia, rheumatoid arthritis, an infection, or gout.

Quality of the Symptoms

Deep knee pain may indicate damage to one of the cruciate ligaments. Generalized pain in the knee region is characteristic of referred pain, or pain from a contusion or partial tear of a muscle or ligament.261 Often a patient with a chronic condition has several complaints, and a historical investigation can help identify the original cause. Patients do not always recognize the significance that an old injury may play in their current condition, but these options must be considered if the clinician is unable to make a diagnosis with the information available.

Reports of Swelling

In the presence of trauma, the main thrust of the history should be to establish whether the patient experienced an effusion or hemarthrosis (the assessment of swelling is described in “Observation” section.) An effusion is the method by which the joint reacts to stress and usually takes several hours to accumulate. The effusion can result from blood filling the joint or from an increased production of synovial fluid. The time frame of onset provides the clinician with clues as to the nature of the effusion. Synovial effusion usually takes 6–12 hours to develop and produces a dull, aching pain as the joint capsule is distended. By contrast, an acute hemarthrosis is usually well formed after 1–2 hours, leaving a very tense and inflamed knee. The two diagnoses that represent over 80% of the causes of an acute tense hemarthrosis are an ACL tear and patellar dislocation.262 Other causes of an intra-articular effusion include MCL rupture and intra-articular fracture. Patients with a meniscal lesion often report repetitive episodes of effusion.259

Reports of Joint Noise

Reports of grinding, popping, and clicking in the knee with a particular maneuver are common but may not be related to a pathologic process.167 However, reports of a “pop” involving sudden rotation of the femur or tibia may indicate damage to the ACL, MCL, coronary ligament, or meniscus, or an osteochondral fracture.167 Sprains to the ligaments of the knee are often more painful than complete ruptures, because the latter have no intact fibers from which pain of a mechanical origin can occur. Instability of the knee often is described as a sensation of “giving way,” sliding, or buckling. Sharp, catching pain usually indicates a mechanical problem.

Aggravating Positions or Activities

Questions should be asked to determine whether certain kinds of activities bring on the symptoms. For example, the pain may be noticed after resting or after certain activities. Morning pain and stiffness that lessens with activity or movement may indicate a degenerative joint complaint. Complaints of locking or pseudolocking during active or passive flexion and extension can highlight a dysfunctional structure. True locking of the knee is rare; however, loose bodies can cause recurrent locking or the sensation of something catching or getting in the way of movement. “Locking” that occurs with extension could indicate a lesion of the meniscus, a hamstring muscle spasm or an entrapment of the cruciate ligament. “Locking” that occurs with flexion could indicate a lesion to the posterior horn of the medial meniscus. With patellar irritability, there is no true mechanical blocking, although there may be stiffness, grating, or rapid movement inhibition.259

Impact on Function

The clinician should determine which functional activities reproduce the pain or exacerbate the symptoms. The following statements should be viewed as generalizations, as there are always exceptions.

• Weight-bearing activities involving a twisting weight-bearing load (e.g., getting in and out of a car with low seats) tend to aggravate a meniscal lesion.
• Patellofemoral joint pain often develops as a result of extended activity, such as in the middle of a long run or bike ride, continues into the evening or night, and can disturb sleep.259
• Walking upstairs or downstairs is usually difficult for patients with knee pathology. Usually, patients with a meniscal lesion complain of increased pain with stair climbing, whereas patients with a patellofemoral joint lesion complain of increased pain when descending stairs.
• Patients with a meniscal lesion or patellofemoral pain rarely can do a full squat without pain.
• Complaints of pain with kneeling activities are more likely to indicate a patellofemoral lesion than a meniscal lesion.
• Sitting tends to provoke more symptoms in patients with patellofemoral dysfunction than it does in those with meniscal or ligamentous lesions.

Anterior Knee Pain

Due to the prevalence of patellofemoral related disorders, there is a significant temptation to cut corners with a patient who presents with anterior knee pain, and to proceed directly to the diagnosis of patellofemoral pain.147 However, this should be avoided, especially in light of the fact that the literature is replete with descriptions of physical examination techniques for the evaluation of the patellofemoral joint.133,226,263–268

Classically, the pain from patellofemoral joint dysfunction is anterior, but it also can be medial,196,272 lateral,196,272 or popliteal (posterior).194 Particular activities can help with differential diagnosis. Pain from rotational malalignment of the patella is typically exacerbated by activity and relieved by rest. Complaints of pain that occur when a patient arises from a seated position, negotiates stairs, or squats are associated with patellofemoral dysfunction. The so-called movie-theater sign196—pain with prolonged sitting—traditionally has been associated with patellar pain from any source. Venous congestion and stretching of painful tissues are potential explanations for this symptom.246 Activities that involve eccentric loading of the knee, and increased hill work with running, tend to provoke patellar tendinitis, whereas inferior patellar pain following vigorous kicking, flip turns in swimming, or delivery of a fast ball in cricket would tend to implicate the fat pad.273 The fat pad also may be irritated with the straight leg raise exercise.266

If a patellofemoral disorder is suspected, the clinician should look for evidence of an anatomical variant and/or a biomechanical dysfunction involving the lower quadrant. These anatomical variants can occur in any of the following joints: hip, patellofemoral, tibiofemoral, subtalar, intertarsal, or any combination of these joints. Examples of biomechanical dysfunctions that can cause patellofemoral disorders include excessive femoral anteversion, excessive genu valgum, excessive tibial external rotation, excessive pronation, and VMO dysplasia.

Edema rarely is reported with insidious onset overuse injuries, except in the case of plical irritation, ITB friction syndrome (ITBFS), irritation of the pes anserine or Osgood–Schlatter's disease.167 Following the history, a hypothesis is made and this hypothesis is then tested with the physical examination. Ideally, the clinician is able to process and identify responsible structures for the patient's complaints and the history of injury to aid in the differential diagnosis.

Systems Review

Knee pain and dysfunction can arise from multiple sources. Knee pain that has gradually worsened over time should lead to an evaluation of systemic illness and overuse complications such as tendinitis. A subjective complaint of stiffness may imply swelling, and the joint mobility and effusion should be assessed. Complaints of weakness should be followed by an examination of the patient's strength and gait pattern.

The clinician needs to consider the likelihood of a specific diagnosis based on age. For example, a slipped capital femoral epiphysis (SCFE) is less likely to be the cause of a recent onset of pain in a 40-year-old fully developed man that it would be in an adolescent. Knee pain can be referred to the knee from the lumbosacral region (L3–S2 segments) or from the hip. For example, anteromedial pain can be referred from the L2 and L3 spinal levels, whereas posterolateral knee pain can be referred from the L4, L5, and S1 to S2 levels. The peripheral nerves are also capable of referring pain to this area. Medial knee pain having a burning quality could indicate saphenous nerve neuritis. A family history of knee problems, rheumatoid arthritis, or OA may need further investigation with a laboratory work-up or X-ray films. Pain that is constant and burning in nature should alert the clinician to the possibility of complex regional pain syndrome (CRPS), gout, or radicular pain. Intermittent pain usually indicates a mechanical problem (meniscus). The health intake questionnaire should be designed to provide evidence of undiagnosed systemic problems that relate to the knee dysfunction (e.g., Lyme disease). Chapter 5 describes some of the more common causes of referred knee pain, and causes of a more serious nature.

Observation

The observation component of the examination begins as the clinician meets the patient and ends as the patient is leaving. This informal observation should occur at every visit.

Swelling or Effusion

The amount of swelling present may provide the clinician with valuable information regarding the internal damage that may have resulted. Diffuse swelling indicates fluid in the joint or synovial swelling, or both. An effusion can be detected by noticing the loss of the peripatellar groove and by palpation of the fluid. A perceptible bulge on the medial aspect suggests a small effusion; this sign may not be present with larger effusions. The swelling is examined with the patient positioned in supine, in the following manner274:

• Patellar ballottement (maximal effusion). Ballottement of the patella is a useful technique for detecting an effusion. Using one hand, the clinician grasps the patient's thigh at the anterior aspect about 10 cm above the patella, placing the fingers medial and the thumb lateral. The patient's knee is extended. With the other hand, the clinician grasps the patient's lower leg about 5 cm distal to the patella, placing the fingers medial and the thumb lateral. The proximal hand exerts compression against the anterior, lateral, and medial aspects of the thigh and, while maintaining this pressure, slides distally. The distal hand exerts compression in a similar way and slides proximally (Fig. 20-8). Using the index finger of the distal hand, the clinician now taps the patella against the femur. In the normal knee joint with minimal free fluid, the patella moves directly into the femoral condyle and there is no tapping sensation underneath the clinician's fingertips. However, in the knee with excess fluid, the patella is “floating”; thus, ballottement causes the patella to tap directly against the femoral condyle. This sensation is transmitted to the clinician's fingertips. A positive test is indicative of a significant synovial effusion or hemarthrosis in the knee joint. However, sometimes, this test can produce false-positive results. When this is the case, the uninvolved side usually tests positive as well.

If there is no swelling but there is evidence of bruising or bleeding into the tibial area, disruption of the joint capsule may be present, or a SCFE, if the patient is an adolescent. Popliteal swelling, which can compress the tibial or common fibular (peroneal) nerves, or both, can produce complaints of paresthesia and anesthesia.

The formal observation of the patient is divided into three sections: standing and walking, seated, and lying examinations.

Patient Standing

The patient is asked to stand with the feet slightly apart and aligned straight ahead. This position can be used to assess overall limb alignment as well as to identify possible foot abnormalities. A careful physical examination of the hip, knee, and ankle is performed, observing for both static restraints, and, to a great degree, dynamic restraints.127 Following this position, the patient is asked to stand with the feet shoulder-width apart. The entire trunk and lower extremities are observed. Areas of atrophy should be noted and correlated with other findings. Common areas include the medial aspect of the quadriceps following trauma, nerve injury, or knee surgery.

Degree of Femoral Retroversion or Anteversion

Femoral retroversion–anteversion is indicated by whether the feet are rotated outward or inward, respectively, in the relaxed standing position. The position of the patella is examined to see whether it looks inward (the so-called squinting patella), which could indicate femoral anteversion. Femoral anteversion results in internal rotation of the femoral sulcus, and an increase in the Q-angle. Femoral anteversion has been associated with abnormal patellofemoral mechanics.147,275 Even if the patella looks straight in the presence of femoral anteversion, it may be held there by tight lateral structures.266

Leg-Length Discrepancy

Compensations for leg-length discrepancies include excessive foot pronation, toeing-out (forefoot abduction), and a flexed knee gait or stance.276,277

Degree of Genu Varum/Genu Valgum

Genu varus (“bow legs”) can be the result of bowing of the tibia or varus at the knee joint. An increased varus moment can contribute to early degeneration of the knee and, when exaggerated, is most often an indication of advanced degenerative joint disease (DJD).278 On the basis of the relationship between the proximal and distal aspects of the femur, a change in the orientation between the shaft and the neck will change the orientation of the tibiofemoral joint, thereby altering the weight-bearing forces through the knee joint. For example, an increase in the normal angle of inclination at the hip (coxa valga) will redirect the femoral shaft more laterally than normal, resulting in a decrease in the normal physiologic valgus angle of the knee (genu varus). This results in a shifting of the mechanical axis to the medial compartment of the knee, increasing the compression forces medially.66

Genu valgus (“knock knees”) can result from a change of angulation of the femur caused by femoral anteversion, tibial torsion, or excessive foot pronation. A valgus knee increases the Q-angle by displacing the tibial tuberosity laterally and can be associated with patellofemoral pain.279

To observe genu varum and genu valgum, the patient is positioned in standing so that the patellae face anteriorly and the medial aspect of the knees and the medial malleoli of both lower extremities are as close together as possible. A distance of 9–10 cm (3.5–4 inches) between the malleoli of the ankles with the knees touching is considered excessive and indicates genu valgum, whereas a distance of 4 cm (1.6 inches) measured between the knees when the ankles are together, indicates genu varum.280–282

Degree of Knee Flexion

A flexed knee in the relaxed standing position is often indicative of arthritic changes of the knee.

Degree of Genu Recurvatum or Hyperextension

Knee recurvatum may be an expression of a generalized ligamentous laxity or may be associated with patella alta.205 Hyperextension of knee produces stress on the posterior capsule, slackening of the ACL, and alterations in the compressive forces acting on the anterior articulating surface of the tibia.278 The anterior compressive forces can cause the inferior pole of the patella to be driven posteriorly into the fat pad, producing an irritation.

Q-Angle Assessment

A properly measured Q-angle can contribute significantly to the evaluation of patellofemoral malalignment. However, relying solely on the Q-angle measurement to determine patellofemoral alignment is an oversimplification. As with other clinical signs, an abnormal value does not necessarily identify the source of pain. The Q-angle itself is not pathologic and is increased in only a small percentage of patients with patellar pain.283

The Q-angle should be assessed dynamically and statically. It is important that this angle be measured in a consistent fashion. The preferred position for this test is the one-legged standing position without shoes. Hyperpronation of the feet can be masked unless the foot and ankle are placed in a subtalar neutral position284 (see Chap. 21). A measurement is then taken using an imaginary line drawn from the ASIS to the center of the patella, and a second line from the tibial tuberosity to the center of the patella (Fig. 20-6). The weight-bearing position can be simulated in a supine patient by dorsiflexing the ankles, extending the knees, and pointing the toes to the ceiling. With the knee flexed to 90 degrees, the tibial tubercle should lie less than 20 mm lateral to the midline of the femur at the upper edge of the femoral condyles; a distance of more than 20 mm indicates an abnormally lateral tubercle.11 Both tight hamstrings and a decrease in ankle dorsiflexion can result in an increase in the dynamic Q angle.188

Degree of Tibial Torsion285

External tibial torsion increases the Q-angle, whereas internal torsion decreases it.147 The vast majority of the studies focusing on anterior knee pain have examined the coronal relationships at the knee (Q-angle, patellar tilt, patellar subluxation). Few studies have addressed the rotational relationships, specifically the rotational orientation of the tibia to the femur.286 This rotational relationship of the tibia to the femur in the transverse plane is referred to as knee version. Knee version often is recognized as a factor in the context of the osteoarthritic knee.287–289 The significance of this rotational characteristic of the knee with anterior pain is that the patella is tethered to the tibia by the infrapatellar tendon and retinaculum, and if the tibia is rotated externally with respect to the femur, the patella will be pulled laterally by virtue of this attachment.286 If the patella is not free to translate laterally, because of its soft tissue attachments and its conformity with the patellar groove, increased pressure may be placed on the lateral facet. This pressure may produce a condition called a lateral patellar compression syndrome.286,290

Tibia‐to-Floor Angle

If the tibia-to-floor angle is 10 degrees or greater, the extremity requires an excessive amount of subtalar joint pronation to produce a plantigrade foot.205

Patella Tendon‐to-Patella Height Ratio

This measurement is best performed radiographically. The patella tendon length should be equal, or slightly longer than the height of the patella.291 If a ratio of greater than 15–20% exists, patella alta should be suspected. If the ratio is less than 15–20%, patella baja should be suspected.

Foot Alignment

An often-neglected feature, which directly impacts the patellofemoral joint, is that of foot alignment. The normal weight-bearing foot exhibits a mild amount of pronation. If the foot pronates excessively, a compensatory internal rotation of the tibia may occur. This produces an increased amount of rotatory stress and dynamic abduction movement at the knee that has to be absorbed through the peripatellar soft tissues at the knee joint.205,226,275,292 These stresses can force the patella to displace laterally.293,294 In addition, a change in the position of the talus can affect the functional leg length. Subtalar supination may cause the leg to lengthen, whereas subtalar pronation shortens the leg.

Gait

Abnormal foot mechanics are manifested during ambulation, and abnormal gait patterns may suggest an underlying condition (see Chap. 6). The gait assessment relative to the knee allows the clinician to identify deviations of the foot, ankle, knee, or hip joint, such as excessive subtalar and midtarsal joint pronation, limited ankle dorsiflexion, tibial or femoral torsion abnormalities, and excessive varus or valgus at the knee, all of which could place the knee structures at risk for further microtrauma.167

During normal gait, the knee should be observed to flex to approximately 15 degrees at initial contact before extending to the neutral position at terminal stance.278 An increase in 5 degrees of pronation at midstance, a period where the foot should be in supination, holds more potential for producing pain than if the 5 degrees occurs during the contact phase.229

Since the joint reaction forces are reported to increase with the magnitude of quadriceps contraction and the knee-flexion angle,295 patients with patellofemoral pain often adopt compensatory gait strategies to reduce the muscular demands at the knee. Evidence in support of this premise was reported by Dillon et al.,296 who found that subjects with patellofemoral pain limited the amount of stance phase knee flexion during level and ramp walking.

An injury to the ACL produces distinct changes in lower extremity biomechanics during gait.297 Although healthy individuals demonstrate an extensor torque at the knee for 10–45% of the stance phase,298–300 gait analysis of individuals with recent ACL deficiency shows functional adaptations in a high proportion of patients, with an extensor torque that lasts for nearly the entire stance phase.298 Other analysis has also shown a decrease in the flexion moment of the knee in the range of 0–40 degrees of flexion in patients who have a chronic tear of the ACL.301,302

When the normal limb moves into the midstance phase, gravity and inertia generate a moment that tends to flex the knee. Since the quadriceps muscles balance this moment, a decrease in the flexion moment suggests a decrease in the quadriceps muscle moment.303 Such a decrease has been noted in both limbs of patients who had only one knee with a torn ACL.302

Andriacchi303 termed this finding the quadriceps-avoidance gait, although not all patients who have a torn ACL have such a gait, and its prevalence appears to be partly related to the time since the injury.304 In activities that involve knee-flexion angles of less than 30 degrees (i.e., those involving normal gait), the quadriceps-avoidance gait is most effective in preventing anterior tibial translation.303,305,306 In activities that involve knee-flexion angles of 40 degrees or more (e.g., jumping or sharp changes in running direction), increased contraction of the hamstrings is effective in preventing anterior tibial translation.154,306–308

Gait adaptations in individuals with ACL injury who have reconstruction surgery are less clear for two reasons297:

1. Very few comprehensive gait analyses have been conducted on this population.

2. The large variations in surgical and rehabilitation procedures and patient characteristics, and in patient compliance with rehabilitation, limit the generalization of these potential results.

Gait can also be affected by genu recurvatum, because during the loading response in gait, an individual with genu recurvatum transfers body weight directly from the femur to the tibia without the usual muscle energy absorption and cushioning of a flexed knee provided. This may lead to pain in the medial tibiofemoral joint (compression) and posterolateral ligamentous structures (tensile). In individuals with quadriceps weakness, compensation may occur by hyperextending the knee to provide greater knee stability.

Patient Sitting

Active Knee Extension

Although formally assessed as part of the active range of motion (AROM) with passive overpressure tests (see later), active knee extension may also be used during the observation phase of the examination. The patient should fully extend the knee from a flexed position. Normally, the patella follows a straight line, or a slight and smooth, gradual, lateral concave “C” curve as the knee extends. The presence of a “J sign,” in which the patella slips off laterally as the knee approaches extension, or apprehension with motion involving lateral or medial stress, is necessary to confirm patellar instability.11

The patella may be compressed with the palm of the hand through the full ROM, as ulcerated lesions can be tender with this provocative test.11 However, care should be taken with this maneuver, because it can provoke pain in otherwise asymptomatic patients.

Distal patellar lesions are often tender with this test in the early degrees of knee flexion, whereas proximal lesions are tender at approximately 90 degrees.11 This information can help guide the clinician with the intervention. Crepitus at the knee is a nonspecific finding and can be associated with both cartilaginous and synovial lesions.11 Although often a concern to patients because they believe it to be indicative of arthritis, crepitus is often a result of tight, deep, lateral retinacular structures and can be improved with retinacular stretching techniques.266

In addition to observing the patella during active knee extension, the clinician should also note any evidence of a quadriceps lag manifested by an inability to fully extend the knee. This lag can result from muscle atrophy, pain, effusion, reflex inhibition, or a loss of mechanical advantage. Quadriceps reflex inhibition has been well documented throughout the literature and is thought to result from pain or effusion, or both, although the exact etiology has yet to be determined.262,309–314

Some of the proposed causes for this reflex inhibition include

• the result of capsular stretching;313
• the result of increased intra-articular pressure.310

In the presence of various pain syndromes, such as CRPS,309 additional muscle inhibition can occur. In most patients, limitations of motion resolve as the pain and effusion dissipate. However, this quadriceps inhibition may allow scar tissue to form while the knee is held in a flexed position. Atrophy of the quadriceps muscle and flexion contracture usually results, and activities of daily living become more difficult to perform. Joint immobilization can complicate all of these factors. Disuse may induce abnormal cross-links between collagen fibers at abnormal locations,315,316 decreasing their extensibility317 and promoting intra-articular and extra-articular scarring.

Patient Lying Supine

Malalignment can be observed on certain the supine, resting patients, whereas in other subjects a dynamic evaluation (walking, jumping, squatting, etc.) is required to detect an abnormal alignment. The lateral pull test can be performed to assess patellar tracking.318 The patient lies supine with the knee extended and the clinician asks the patient to perform an isometric quadriceps contraction. The clinician observes patellar tracking during the contraction. The test is considered positive if the patella tracks more laterally than superiorly, and negative if superior displacement is equal to lateral displacement.318 However, since the lateral pull test has been found to have only fair intrarater, and poor interrater reliability, care must be taken in placing too much emphasis on this test when making clinical decisions.

Hip Screening

With the patient supine and then prone, the hip is flexed and rotated as the clinician checks for a source of referred pain.196

Since patellar malalignment can be associated with adaptive shortening, the following structures (in decreasing order of frequency) are assessed187,196:

• Lateral retinaculum (see “Special Tests” section). A tight lateral retinaculum may pull the patella laterally.
• Hamstrings (see “Special Tests” section). When an individual with tight hamstrings runs, there is a decrease in stride length and a potential for the quadriceps to fatigue in an effort to overcome the passive resistance of the hamstrings.319 Tightness of the hamstrings also produces an increase in knee flexion at heel strike. Since the knee cannot straighten, an increased dorsiflexion is required to position the body over the planted foot.266 If the range of full dorsiflexion has already occurred at the talocrural joint, further range is achieved by subtalar pronation. This has the effect of increasing the valgus vector force and the dynamic Q-angle.266,320
• Iliotibial band (see “Special Tests” section). The ITB is maximally taut at 20–30 degrees of flexion. Adaptive shortening of this band can cause a lateral tracking and tilting of the patella, and often a stretching of the medial retinaculum.229
• Tensor fascia latae and rectus femoris (see Chap. 19). Adaptive shortening of these structures can increase the amount of compression of the patella on the femur.229
• Hip rotators. The hip rotators can accentuate anteversion or retroversion (see Chap. 19).229
• Achilles–Soleus Length. A decrease in talocrural joint dorsiflexion ROM may result in a compensatory subtalar pronation during ambulation and weight-bearing.321 Soft tissue tightness is particularly prevalent during the adolescent growth spurt, in which the long bones are growing faster than the surrounding soft tissues.322

Active Range of Motion

ROM testing for the tibiofemoral joint should include assessment of knee flexion and extension, tibial internal and external rotation. Normal knee motion (Table 20-7) has been described as 0 degrees of extension to 140 degrees of flexion, although hyperextension is frequently present to varying degrees.323 In general, however, the best way to ascertain normal motion is to examine the contralateral knee, provided that it has no abnormal conditions.

The ROM testing can often be diagnostic and provides the clinician with some clues as to the cause of the problem. Examining the uninvolved knee first allays a patient's fears and helps to determine what the normal ROM is. In addition, observation of the uninvolved knee can afford the clinician information about the patellofemoral joint and the tracking of the patella.324

A number of studies have demonstrated that goniometric measurements of knee ROM performed in a clinical setting can be highly reliable.326–330 Rothstein et al. showed that intratester and intratester reliability for flexion of the knee was high (r = 0.91–0.99 and r = 0.88–0.97, respectively).326 Watkins et al. showed that the intertester reliability for measurements of knee ROM obtained by visual estimation was 0.83 for flexion and 0.82 for extension.330

Flexion

The amount of knee flexion should be assessed to see if the motion is restricted by tight structures. If no restriction is suspected, tests are required for generalized ligament laxity and for abnormally loose patellar retinacula (see later discussion).

The primary flexors of the knee are the three hamstring muscles, assisted by the gracilis, sartorius, popliteus, and gastrocnemius muscles, and the TFL (in 45–145 degrees of flexion; see Table 20-2). The patient lies in the supine position. Using one hand, the clinician grasps the anterior aspect of the patient's lower leg, just proximal to the malleoli, while the other hand grasps the anterior aspect of the patient's thigh, just above the patella. The patient's hip is flexed to about 90 degrees and stabilized with one hand, while the clinician flexes the knee with the other hand (Fig. 20-9). At the end of the ROM, the clinician exerts slight overpressure. The normal end-feel is usually one of soft tissue approximation. A flexion limitation other than soft tissue approximation is usually the result of an articular lesion, such as arthritis or arthrosis (capsular pattern), a lesion of one of the menisci, or a loose body.274

Rotation of the tibia relative to the femur is possible when the knee is flexed and non–weight-bearing, with rotational capability greatest at approximately 90 degrees of flexion.97

Extension

The primary extensors of the knee are the quadriceps muscles, consisting of the rectus femoris, VL, vastus medialis, and vastus intermedius (see Table 20-2). Also assisting with knee extension in the 0–30-degree flexion range is the ITB and TFL.

The patient extends the knee (see Fig. 20-10), and the clinician applies overpressure by stabilizing the thigh and pulling the ankle up to the ceiling, while allowing the conjunct external rotation of the tibia. Under normal conditions, the end-feel is usually hard.

A limitation of active knee motion can have a number of causes. The patient may have a neurologic deficit from a lumbar intervertebral disk (IVD) herniation, with loss of knee motion as the primary symptom. Any acute injury causing pain may limit active knee motion as a result of muscle inhibition.310

Passive Range of Motion

Passive movements, as elsewhere, can determine the amount of available motion, the presence or absence of a capsular pattern, and the end-feel. At the tibiofemoral joint, the end-feel of flexion should be tissue approximation, whereas the end-feel of extension and medial and lateral rotation of the tibia on the femur is tissue stretch. Passive hyperextension of the knee with overpressure is performed to assess (from the end-feel) whether the knee extension is limited as a result of an articular disorder. Such articular disorders include arthritis or arthrosis, a lesion of one of the menisci, or a loose-body involvement. Hayes et al.331 found the intrarater reliability of end-feel and pain/resistance judgments at the knee to be generally good, especially after accounting for subject change and unbalanced distributions. Interrater reliability, however, was generally not acceptable, even after accounting for these factors.331 In a separate study, Hayes et al.332 explored the construct validity and test–retest reliability of the passive motion component of the Cyriax soft tissue diagnosis system and compared the hypothesized and actual patterns of restriction, end-feel, and pain/resistance sequence (P/RS) of 79 subjects with OA of the knee and examined associations among these indicators of dysfunction and related constructs of joint motion, pain intensity, and chronicity. The results of the study are discussed next.

Consistent with the hypotheses based on Cyriax's assertions about patients with OA, most subjects had capsular end-feels for extension; subjects with tissue approximation end-feels for flexion had more flexion ROM than did subjects with capsular end-feels, and the P/RS was significantly correlated with pain intensity (ρ = 0.35, extension; ρ = 0.30, flexion).332

Contrary to the hypotheses based on Cyriax's assertions, most subjects had noncapsular patterns, tissue approximation end-feels for flexion, and what Cyriax called pain synchronous with resistance for both motions.332

Pain intensity did not differ depending on end-feel. The P/RS was not correlated with chronicity (ρ = 0.03, extension; ρ = 0.01, flexion).332

Reliability, as analyzed by ICCs (ICC[3,1]) and Cohen's κ coefficients, was acceptable (≥0.80) or nearly acceptable for ROM (ICC = 0.71–0.86, extension; ICC = 0.95–0.99, flexion) but not for end-feel (κ = 0.17, extension; κ = 0.48, flexion) and P/RS (κ = 0.36, extension; κ = 0.34, flexion).332

The study concluded that the use of a quantitative definition of the capsular pattern, end-feels, and P/RS as indicators of knee OA should be reexamined and the validity of the P/RS as representing chronicity and the reliability of end-feel and the P/RS are questionable.332

Others have found that a ratio of loss of extension to loss of flexion during passive range of motion (PROM) of between 0.03 and 0.50 was more likely than a noncapsular pattern in patients with an inflamed knee or osteoarthrosis (likelihood ratio = 3.2).333

According to the osteopathic theories of somatic dysfunction,334 the following guidelines are used:

• If the restriction to movement is opposite to the direction that the bone seems to have traveled (e.g., the tibia has a reduced joint glide), a mobilization or a manipulation is the intervention of choice.
• If the restriction to movement is in the same direction that the bone seems to have moved and the opposite movement seems to be excessive (a change has occurred in the overall starting position), a muscle imbalance should be suspected, and a muscle energy technique used.
• If the patient demonstrates normal range but pain with movement, the joint cannot be at fault.
• If a muscle is very hypertonic, a spinal dysfunction may be present (unless trauma is involved), producing a hypermobility.

Even minor losses of knee motion may have adverse effects. It is common to lose both flexion and extension; however, loss of extension is usually more debilitating.335 A loss of extension of more than 5 degrees may cause patellofemoral pain and a limp during walking,336 whereas restricted flexion does not severely affect gait as long as the knee can be flexed to at least 60 degrees. 337 Diminished running speed is associated with loss of flexion of 10 degrees or more,338 whereas an extension deficit of more than 10 degrees is poorly tolerated by active people.339 A loss of more than 20 degrees of extension may cause a significant functional limb-length discrepancy.338

Patellar Motion Tests

Probably the most important part of the patellofemoral examination is the observation of the dynamics of patellar tracking in weight-bearing and non–weight-bearing.

A unilateral squat (Waldron test) can be used to assess patellofemoral function.340 The patient stands on the involved leg, and the clinician sits or squats next to the patient. Using the entire surface of the palm, the clinician exerts slight pressure in an anteroposterior direction against the patient's patella (Fig. 20-11). From this position, the patient is asked to bend the knee slowly, if possible, to about 90 degrees, while the clinician palpates for crepitus and locking of the patella and assesses the course of movement of the patella. Crepitus or locking can indicate the presence of patellofemoral chondropathy or patellofemoral arthrosis. However, Nijs et al.341 reported unimpressive positive and negative likelihood ratios for this test.

In patellar malalignment or pathologies of the corresponding femoral joint surface, movement of the patella can be disturbed. The patella is observed while the patient initiates flexion of the knee to see if it engages smoothly at the proximal end of the trochlea or more distally than normal. Lateralization of the patella can occur during flexion, particularly when the Q-angle is excessive.

The passive mobility tests for the patella are outlined in “Patellar Stability Tests” section.

Kinetic Chain Assessment

Ankle Motions

Ankle motions are tested because, as has been discussed, a number of structures share a common relationship with the foot, ankle, and knee joint complex (see Chap. 21) and can therefore have an impact on knee function. For example, adaptive shortening of the gastrocnemius, particularly in the presence of adaptively shortened hamstring muscles, may produce increased knee flexion at initial contact and during the stance phase of gait.215

Hip Motions

Several muscles cross both the hip and the knee. These include the rectus femoris, gracilis, sartorius, and hamstrings muscles. Adaptive shortening of any of these structures may cause alterations in postural mechanics and gait. The hip rotators can also influence other aspects of the lower kinetic chain. Sahrmann advocates the testing of length–strength relationship of the hip external rotators because of their CKC function of decelerating lower extremity internal rotation.167,342

Passive Accessory Motion Testing

The passive accessory motion tests, or joint glides, are performed at the end of the patient's available range to determine if the joint itself is responsible for the loss of motion.

Tibiofemoral Distraction

The patient lies in the prone position. The clinician is beside the patient. Using one hand to stabilize the thigh, the clinician uses the other hand to grip the distal tibia from the medial and lateral sides. The clinician then applies a force perpendicular to the tibial joint surface (Fig. 20-12).

Posterior Glide of the Tibia on the Femur

The patient lies in the supine position with the thigh supported by a towel. Standing to the side of the patient, the clinician applies a posterior glide through the tibia (Fig. 20-13).

Anterior Glide of the Tibia on the Femur

The patient lies in the supine position with the knee flexed and the foot placed on the table. The clinician stands to the side of the patient. Using both hands, the clinician applies an anterior glide of the tibia (Fig. 20-14).

Proximal Tibiofibular Joint

The proximal tibiofibular joint can be assessed with the patient in the supine position and the knee flexed to approximately 90 degrees. The clinician stabilizes the tibia using one hand and uses the other hand to grasp the fibular head and to assess the anterolateral and posteromedial glides (Fig. 20-15).

Passive Tibial External Rotation

The patient lies in the supine position. Using one hand, the clinician grasps the patient's foot and brings the ankle into maximal plantar flexion. The other hand is positioned to monitor the joint space.274 The patient's knee is flexed to 90 degrees and the hip to approximately 45 degrees. The distal hand performs an external rotation of the tibia while maintaining the ankle in maximum plantar flexion (see Fig. 20-16). At the end of the ROM, the clinician exerts slight overpressure. Under normal conditions, the end-feel is firm. The clinician notes whether the pain is provoked or whether there is a hypermobility or hypomobility274:

• Pain with passive external rotation of the tibia can be the result of a lesion of the medial meniscotibial ligament, medial meniscus, MCL, or the posteromedial capsuloligamentous complex.
• Hypermobility with this maneuver can be the result of a lesion of the posteromedial capsuloligamentous complex, often in combination with lesions of the MCL and the ACL. Hypermobility may also be seen in ballet dancers.
• Hypomobility of passive tibial external rotation is seen only in severe articular disorders with significant capsular limitations of motion.

Passive Tibial Internal Rotation

The patient lies in the supine position. Using one hand, the clinician grasps the patient's foot and brings the ankle into maximal plantar flexion. The other hand is positioned to monitor the joint space. The patient's knee is flexed to 90 degrees and the hip to about 45 degrees. The distal hand performs an internal rotation of the tibia while maintaining the ankle in maximum plantar flexion (see Fig. 20-17). At the end of the ROM, the clinician exerts slight overpressure. Under normal conditions, the end-feel is firm. The clinician notes whether pain is provoked or whether there is hypermobility or hypomobility274:

• Pain can be the result of a lesion of the lateral meniscotibial ligament, lateral meniscus or posterolateral capsuloligamentous complex.
• Hypermobility can be the result of a lesion of the posterolateral capsuloligamentous complex.
• Hypomobility is seen only in severe articular disorders with significant capsular limitations of motion.

Patellofemoral Joint Mobility Tests

The patient lies in the supine position with the involved knee supported in slight flexion. The clinician moves the patella superiorly, inferiorly, medially, and laterally (Fig. 20-18). Caution must be used with the lateral glide in case the joint is hypermobile, as this is the most common direction for patella dislocations. To assess the various tilts of the patella, both hands are wrapped around the patella and the thumbs are used to tilt the patella medially and laterally (Fig. 20-19). The findings are compared with the contralateral side.

Strength Testing

Gross muscle testing is useful in checking for deficits in the lower extremities. Strength testing involves the performance of resisted isometric tests. The joint is placed in its resting position to minimize any joint compression forces.

Knee Flexion

The strength of the knee flexors (the hamstrings) can be assessed by positioning the patient prone with the knee flexed to approximately 80–90 degrees. By internally rotating the tibia (Fig. 20-20) and resisting knee flexion, the clinician can theoretically assess the integrity of the medial hamstrings (semimembranosus and semitendinosus). The biceps femoris is assessed similarly by externally rotating the tibia and resisting knee flexion (Fig. 20-21).

Knee Extension

Pain may be reproduced, and localized, with multiple angle isometric testing of the quadriceps, as described by McConnell.189 Thus, the strength of the knee extensors (the quadriceps) is tested in 0, 30, 60 (Fig. 20-22), 90, and 120 degrees of knee flexion and held for 1 second with the femur externally rotated, to see if the pain can be reproduced or localized. The reproduction of pain with these tests suggests excessive pain from patellar compression. Any abnormal tibial movement with these tests may suggest ligamentous instability.343 If pain is noted during this testing, McConnell suggests returning the knee to full extension, producing and maintaining a medial glide of the patella, and then returning the knee to the painful position to retest. This action should reduce the pain if it is of a patellofemoral origin.189

The final 15 degrees of knee extension require a 60% increase in muscle firing.137 An extension lag (passive knee extension that is greater than active knee extension) indicates a slight loss of quadriceps muscle function.167,266,344

Siegel and Jacob343 suggest testing the quadriceps muscle at 0, 30, 60, and 90 degrees while observing for any abnormal tibial movement. Any abnormal tibial movement would suggest ligament instability or excessive pain from patellar compression.

Plantar Flexion

The heel raise can be used to assess the strength of the gastrocnemius. The strength of the gastrocnemius muscle is tested because of its intimate relationship to the knee and its importance in lower extremity function. The patient is positioned in standing, leaning against a wall, or supported by the clinician with the knees extended. One foot is tested at a time as the patient rises up on the toes for 10–20 repetitions (depending on age and physical ability) while standing.

• The patient everts the foot and raises up on the toes to test the lateral head.
• The patient inverts the foot and raises up on the toes to test the medial head.

The soleus muscle can be tested similarly by having the patient perform a unilateral heel raise while keeping the knee flexed.

Palpation

Palpation of the soft tissues about the knee is critical and often reveals more important information than any imaging tool. For palpation to be reliable, the clinician must have a sound knowledge of surface anatomy (Figs. 20-23 and 20-24), and the results from the palpation examination should be correlated with other findings. A logical sequence should be employed by the clinician. The skin, retinacula, quadriceps tendon, and patellar tendon are palpated to rule out any soft tissue sources of pain. Differences in temperature between the knees suggest inflammation in the warmer of the two. The following structures should be identified and palpated.

Posterior Aspect

The patient lies in the prone position. The clinician locates the popliteal fossa. The semimembranosus and semitendinosus form the proximal medial border of the fossa. Deep inside this fossa, a Baker's cyst can be palpated if it is present. With the knee in a slightly flexed position, the thin round tendon of the semitendinosus should be easy to palpate. Medial and lateral to this tendon are the deeper parts of the semimembranosus. The popliteal pulse can be located just below the crease of the knee, more to the lateral side than to the medial side, and posterior to the tibial plateau. Medial to the pulse is the tendon of semimembranosus. At this point, if the thumb is pushed deeper, the attachment of the PCL can be located as it arises from the back of the tibia. Even under normal circumstances, this attachment will be tender. A little lateral to this is the attachment of the meniscofemoral ligament. The PCL and meniscofemoral ligament curve inward, to attach on the inner aspect of the medial condyle of the femur.

At the proximal lateral part the fossa, the biceps femoris tendon is found. This tendon is palpable together with the common fibular (peroneal) nerve. The tendon of the gracilis is medial and anterior to the medial part of the semimembranosus. Palpation performed medially and anteriorly to this point leads to the sartorius muscle. The tendons of the sartorius, gracilis, and semitendinosus form the pes anserinus. The sartorius and gracilis muscles can be differentiated as follows: the gracilis contracts during hip adduction, while the sartorius contracts during hip abduction. Palpation more anteriorly leads to the medial femoral condyle and the adductor tubercle. Tenderness at the anterior aspect of the medial femoral condyle, associated with a snapping sensation as the knee is flexed, can indicate a symptomatic plica.345 The adductor tubercle serves as the attachment site for the patellar retinaculum and the medial patellofemoral ligament, and is a hallmark site of tenderness with lateral patellar dislocation.274 The adductor tubercle is also the attachment site of the adductor magnus, and the origin of the MCL. The distal borders of the popliteal fossa are palpated by positioning the patient's knee in slight flexion. The medial head of the gastrocnemius can be palpated deep within and medial to the fossa, while the lateral head can be found deep within and medial to the tendon of the biceps femoris muscle.

Anterior Aspect

The patient lies supine with the hip and thigh positioned in extension. The clinician palpates the medial and lateral edges of the patella. The VMO normally inserts into the upper third or half of the medial patella and is readily palpable. In patients with patella malalignment, the VMO may be dysplastic and virtually invisible inserting proximal to the superior pole of the patella.346 Palpation of the rectus femoris insertion on the superior aspect of the patella is only possible with the patella tipped slightly forward.274 Complaints of pain distal to the patella during extension of the knee may indicate a patella tendon–ligament lesion at the inferior pole. In some individuals, the continuation of the tendon of the VL muscle, the lateral patellar retinaculum, can be palpated at the lateral side of the patella.274

Palpation of the joint space is made easier when the tibia is rotated internally and externally while in the flexed position. The anterior part of the medial meniscus is palpable in the medial joint space with the tibia externally rotated, between the patellar tendon–ligament and the anterior edge of the MCL. Under normal circumstances, the medial meniscus is not palpable beyond 30 degrees of flexion.274 The medial meniscotibial or coronary ligament, which attaches the medial meniscus to the tibia, is palpable anteriorly with the knee positioned at 90 degrees of flexion and the tibia maximally externally rotated, proximal to the tibia (passive external rotation of the knee will provoke the patient's pain, if the ligament is damaged).274

Other structures to palpate for tenderness on the anterior aspect of the knee include the following:

• Base (inferior pole) of patella. Tenderness at the inferior tip of the patella indicates patellar tendinitis.
• Infrapatellar fat pad (Hoffa's fat pad). This structure is located between the patella ligament (anteriorly) and the anterior joint capsule (posteriorly).
• Lateral retinaculum.
• Apex of patella.
• Accessory retinaculum from the ITB.
• Medial retinaculum.
• Medial and lateral patellar facets. These facets, which are readily palpated using the thumb and index finger, can be tested for tenderness and alignment, as can the overhang of the lateral facet over the patellar groove, by pushing the patella to one side and then the other (glide test), and then curling the fingers around and under the borders of the patella. Palpation of the facets should not elicit pain. The clinician should be able to palpate under one-third of the patella. A tilt of the patella (lateral side down) reflects a tight retinaculum, especially if the tilt cannot be passively corrected by the clinician.346 When the patella is laterally displaced by the clinician and the patient reports sudden and considerable discomfort as the knee approaches extension, this is termed the apprehension sign (see “Special Tests” section).346 The combination of tilt and lateral facet tenderness in the absence of any other positive findings on physical examination suggests clinically significant patella malalignment.346
• Dynamic restraints. The patient is asked to contract the quadriceps. In patients with malalignment, the VMO typically cannot be identified by sight or palpation; it inserts no farther distally than the proximal pole of the patella and it remains soft, even with maximal quadriceps contraction.196 In the normal knee, the VMO should be felt to contract simultaneously with the VL.

Lateral Aspect

The fibular head can be palpated by following the tendon of the biceps femoris distally. It is often more distal and posterior than imagined. On the lateral side, the highest point on the lateral femoral condyle is the lateral epicondyle, which serves as the origin of the LCL. The LCL is best palpated when the hip is maximally externally rotated and the knee is flexed to 90 degrees in the “figure-four” cross-legged stance.274 If the LCL is followed down to the fibular head, it will be felt to blend with the biceps femoris. On the posterolateral aspect of the condyle is the attachment for the lateral head of the gastrocnemius. Anterior to this, there is a small circular groove, which is where the tendon of the popliteus originates from the lateral condyle. Tenderness in this location, just behind the LCL, either anterior or posterior to it, would suggest damage to the popliteus muscle.274 On the anterolateral aspect of the knee is Gerdy's tubercle, the largest bony prominence medial to the apex of the fibular head, which serves as the attachment site for the ITB.

The lateral joint space is palpated starting at a point just lateral to the patellar tendon–ligament. The anterior part of the lateral meniscus is best palpated with the knee in an extended position.

Medial Aspect

The highest point of the medial aspect of the femur is the medial epicondyle, which serves as the origin for the MCL. Superior to this point is the adductor tubercle, and superior to that is the supracondylar ridge, which is the attachment for the VMO. Very localized tenderness at the medial aspect of the knee, away from the joint line, may indicate a neuroma.344

Special Tests

Numerous special tests exist for the knee joint complex based on the intent and diagnostic purpose.

Stress Tests

The stress tests are used to determine the integrity of the joint, ligaments, and the menisci. A complete history and physical examination can diagnose approximately 90% of ligamentous injuries. The goal of the stress tests is to identify the degree of separation and the quality or end-feel of the separation when a stress is applied in a specific direction. Intact ligaments have an abrupt and firm end-feel, whereas sprained ligaments have a soft or indistinct end-feel depending on the degree of injury. A comparison should always be made with the uninvolved knee before a determination is made. It is important to remember that both pain and swelling can hamper the sensitivity of these tests.347

Serious functional instability of the knee appears to occur unpredictably. The reasons for such discrepancies are unknown, but they may be a result of36

• varying definitions of instability;
• varying degrees of damage to the ACL;348,349
• different combinations of injuries;71
• different mechanisms of compensation for the loss of the ACL;
• differences in rehabilitation;
• the diverse physical demands and expectations of different populations.

Valgus Stress

The patient lies in the supine position, with the involved knee extended. The clinician applies a strong valgus force, with a counterforce applied at the lateral femoral condyle (Fig. 20-25). Normally, there is little or no valgus movement in the knee, and, if present, it should be less than the amount of varus motion. Under normal conditions, the end-feel is firm. With degeneration of the medial or lateral compartments, varus and valgus motions may be increased, while the end-feels will be normal.

With the knee tested in full extension, any demonstrable instability is usually very significant. Pain with this maneuver is caused by an increase in tension of the medial collateral structures or the connection of these structures with the medial meniscus. If pain or an excessive amount of motion is detected compared with the other extremity, a hypermobility or instability should be suspected. The following structures may be implicated:

• Superficial and deep fibers of the MCL
• Posterior oblique ligament
• Posteromedial capsule
• Medial capsular ligament
• ACL
• PCL

To further assess the MCL, posterior oblique ligament, and PCL, the test is then repeated at 20–30 degrees of flexion. Hughston55 concluded that a valgus stress test positive at 30 degrees and negative at 0 degree indicates a tear limited to the medial compartment ligaments (posterior oblique ligament) and posterior medial capsule, whereas a valgus stress test positive at 0 degree indicates a tear of both the PCL and the medial compartment ligaments.

The posterior fibers of the MCL can be isolated, by placing the knee in 90 degrees of flexion with full external rotation of the tibia.274 The femur is prevented from rotating by the clinician's shoulder. The clinician places one hand on the posterior aspect of the foot and the other on the heel, and an external rotation force is applied using the foot as a lever.

These tests can be graded by the following:63

• Grade I: The joint space opening is within 2 mm of the contralateral side.
• Grade II: The joint space opens 3–5 mm more than the contralateral side in 20 degrees of knee flexion and less than 2 mm more than the normal knee in full extension.
• Grade III: The joint space opens 5–10 mm more than that of the normal knee in 20 degrees of flexion and full extension.

More research is needed to evaluate the diagnostic accuracy and reliability of this test.

Varus Stress

The patient lies in the supine position, with the involved knee in full extension. The clinician applies a strong varus force, thereby gapping the lateral aspect of the knee (see Fig. 20-26). To be able to assess the amount of varus movement, the clinician should repeat the maneuver several times, applying slight overpressure at the end of the ROM. Under normal conditions, the end-feel is firm, after slight movement. Unlike the valgus stress test, the varus test has been shown to be highly unreliable with many false-negative findings.351

Theoretically, if this test is positive for pain or excessive motion compared with the other extremity, the following structures may be implicated:

• LCL
• Lateral capsular ligament
• Arcuate-popliteus complex
• ACL
• PCL

If the instability is gross, one or both cruciate ligaments as well as, occasionally, the biceps femoris tendon and the ITB may be involved, leading to a rotary instability if not in the short term, certainly over a period of time.159

The test is then repeated at 10–30 degrees of flexion with the tibia in full external rotation to further assess the LCL, posterolateral capsule, and arcuate–popliteus complex.

Grading of these injuries is the same as for MCL injuries and is based on the degree of opening of the lateral joint line.63

More research is needed to evaluate the diagnostic accuracy and reliability of this test.

One-Plane Anterior Instability

Ensuring the integrity of the ACL is crucial for maintaining the normal biomechanical properties of the knee joint, protecting its periarticular structures, and preventing premature OA. Knee joints with ACL deficiencies have rotary instabilities that expose supporting ligaments and menisci adjacent to the ACL to further damage and degenerative joint disease.28 Signs and symptoms of chronic rotary knee instabilities from ACL deficiencies include swelling, pain, a “giving way” of patients' knee joints, arthritis, and possible subsequent meniscal injuries.

Several tests have been advocated for testing the integrity of the ACL. Three of the more commonly used ones are the Lachman test, the anterior drawer test, and the pivot shift (see “Anterolateral Rotary Instability” section).

Lachman Test

Torg et al.352 were the first to publish a description of the Lachman test, whereby the knee is held in 30 degrees of flexion while the tibia is anteriorly translated with respect to the femur (Fig. 20-27).

The accuracy and reliability of the Lachman appears to vary. Katz et al. found that in the hands of an experienced clinician, accuracy of this test was 81.8% sensitive and 96.8% specific,353 increasing to 100% if the patient was anesthetized.354,355 In contrast, Cooperman et al.356 reported that the predictive value of a positive test was 47% for all examiners, whereas the predictive value of a negative test was 70%, results that would indicate that Lachman test judgments have limited reliability and may be more useful for predicting that a patient does not have an ACL injury than for predicting that the ACL is injured.357

These discrepancies likely occur as there are a number of factors that can influence the results. These include

• an inability of the patient to relax;
• the degree of knee flexion;
• the size of the clinician's hand;
• the stabilization (and thus relaxation) of the patient's thigh.

According to Weiss et al., 358 these factors can be minimized by the use of the modified Lachman test. In this modification, the patient lies in the supine position, with the feet resting firmly on the end of the table and the knees flexed 10–15 degrees. The clinician stabilizes the distal end of patient's femur using the thigh rather than the hand, as in the Lachman test, and then attempts to displace patient's tibia anteriorly. If the tibia moves forward, and the concavity of the patellar tendon–ligament becomes convex, the test is considered positive.

The grading of knee instability is as follows55,359,360:

• 1 + (mild): 5 mm or less
• 2 + (moderate): 5–10 mm
• 3 + (serious): more than 10 mm

With this test, false-negatives can occur. False-negatives may be caused by a significant hemarthrosis, protective hamstring spasm, or tear of the posterior horn of the medial meniscus.352

Active Lachman Test

The patient lies in the supine position with a bolster under the distal femur so that the knee is flexed to 30–40 degrees. The patient is asked to actively extend the involved knee and then to relax back to the starting position. A positive test for a torn ACL is indicated by an anterior glide of the proximal tibia during the knee extension. The one study361 that examined this test did not report reliability or diagnostic accuracy.

Anterior Drawer Test

The aforementioned Lachman test is a modification of the anterior drawer test.274 The patient lies in the supine position with the clinician standing to the side of the patient's involved knee. The clinician grasps the lower leg of the patient just distal to the joint space of the knee and the patient's knee is flexed to 90 degrees so that the foot is flat and the lower leg is not rotated. The clinician fixates the patient's leg by sitting on the foot. The clinician can place the thumbs either in the joint space or just distal to it to assess mobility. The clinician tests the tension in the musculature. It is important that all muscles around the knee be relaxed to allow any translatory movement to occur. With both hands, the clinician now abruptly pulls the lower leg forward (Fig. 20-28). This test is positive for an ACL tear when an abnormal anterior movement of the tibia occurs compared with the other extremity. Overall, there is wide variation in the reported sensitivities of the anterior drawer test. The anterior drawer test in 80 degrees of flexion without rotation has been found to be 40.9% sensitive and 96.8% specific.353 This test appears to be a specific test helpful at ruling in a torn ACL when the test is positive.352,362,363 False-negatives may occur with this test for the same reasons as those in the Lachman test. Given the low sensitivity of this test, the clinician should not rule out an acute ACL injury solely on the basis of a negative anterior drawer.

There are a number of variations to the anterior drawer test, all of which involve positioning the patient supine274:

• Anterior drawer test and maximal external rotation.274 The initial positions of the patient and clinician are the same as in the anterior drawer test in 80 degrees of flexion without rotation, except that the lower leg is positioned in maximum external rotation. For the performance, refer to the preceding description. The ACL and the medial and posteromedial capsuloligamentous structures are tested in this position. If this test is positive, there is likely to be an anteromedial rotatory instability. The specific medial and posteromedial structures that are affected can be further differentiated by the abduction (valgus) stress tests previously described. No diagnostic accuracy studies have been performed to determine the sensitivity and specificity of this test.
• Anterior drawer test and maximal internal rotation.274 The initial positions of the patient and clinician are the same as in the anterior drawer test in 80 degrees of flexion without rotation, except that the lower leg is now maximally internally rotated. Performance of the test is the same as described earlier for that test. When in maximal internal rotation, the PCL can completely restrict anterior translation of the tibia. Thus, for this test to demonstrate excessive anterior translation, the PCL, ACL, and lateral or posterolateral capsuloligamentous structures have to be affected. No diagnostic accuracy studies have been performed to determine the sensitivity and specificity of this test.

Comparison of the Lachman and Anterior Drawer Tests

The Lachman test has two advantages over the anterior drawer test in 90 degrees of knee flexion. First, all parts of the ACL are more or less equally taut. Second, in acute lesions it is often impossible to position the knee in 90 degrees of flexion because of a hemarthrosis. In a study of patients with an ACL rupture, the Lachman test was positive in 80% of nonanesthetized patients and 100% of anesthetized patients. In comparison, the anterior drawer sign was positive in 9% of nonanesthetized patients and 52% of anesthetized patients.364

Jonsson et al.365 compared both the Lachman and anterior drawer tests in 45 patients with an acute ACL injury and 62 patients with a chronic knee injury. Patients were tested while nonanesthetized and anesthetized, and the diagnosis was verified by arthroscopy. The Lachman test results for the acute injury group was 87% (conscious) and 100% (anesthetized). The anterior drawer test results were 33% and 98%, respectively. The chronic injury group scored a positive Lachman test in 97% (conscious) and 99% (anesthetized). The anterior drawer test was positive in 92% and 100%, respectively.

According to Larson,366 the Lachman test proved to be the most sensitive test for an ACL rupture. However, this article lacked statistical data to verify this assertion. Another study355 that compared the two tests reported a sensitivity of 99% for the Lachman test and a sensitivity of 70% for the anterior drawer sign.

One-Plane Posterior Instability

The PCL is very strong and is rarely completely torn. It is typically injured in a dashboard injury or in knee flexion activities (falling on the patella). Several tests have been advocated to test the integrity of the PCL.274

Posterior Sag (Godfrey) Sign

The patient lies in the supine position with the knees flexed to approximately 90 degrees and the legs supported under the lower calf/heel by the clinician's arm. The clinician assesses the contour of the tibial tuberosities (Fig. 20-29). If there is a rupture (partial) of the PCL, the tibial tuberosity on the involved side will be less visible than that on the noninvolved side.367 This discrepancy is caused by an abnormal posterior translation, resulting from a rupture of the PCL. In cases of doubt, the patient can be asked to contract the hamstrings slightly by pushing the heels into the clinician's arm. This maneuver usually results in an increase in the posterior translation of the tibia and is often performed as a quick test of the integrity of the PCL. This test may have some value as a screening test when negative due to its high sensitivity.368,369

Posterior Drawer Test

The patient lies in the supine position, with the involved knee flexed to 90 degrees. The clinician attempts a posterior displacement of the tibia on the femur (Fig. 20-30). In a blinded, randomized, and controlled study involving 39 patients to assess the clinical examination skills of orthopaedic surgeons with fellowship training in sports medicine, Rubinstein et al.370 reported that the accuracy for detecting a PCL tear was 96%, with a 90% sensitivity and a 99% specificity. The examination accuracy was higher for grades II and III posterior laxity than for grade I laxity.370 Eighty-one percent of the time, the examiners agreed on the grade of the PCL tear for any given patient.370

Functional Posterior Drawer Test.371

The patient lies in the prone position with the foot in neutral rotation and the knee flexed to 80–90 degrees. The patient is asked to isometrically contract the hamstrings while the clinician stabilizes the foot (Fig. 20-31). A positive result for a PCL tear is a posterior subluxation of the lateral tibial plateau.

Quadriceps Active Test

The patient lies in the supine position and the relaxed limb is supported with the knee flexed to 90 degrees in the drawer-test position. The patient is asked to execute a gentle quadriceps contraction to shift the tibia without extending the knee. If the PCL is ruptured, the tibia sags into posterior subluxation (∼2 mm or more), and the patellar ligament is then directed anteriorly. Studies have shown significantly different sensitivities for this test. Rubinstein et al.370 reported a sensitivity of 54% and a specificity of 97% whereas Daniel372 reported a sensitivity of 98%.

Rotary Instabilities

Rotary or complex instabilities occur when the abnormal or pathologic movement is present in two or more planes. The ligamentous laxities present at the knee joint in these situations allow motion to take place around the sagittal, coronal, and horizontal axes.

Posterolateral Instability

This type of instability is relatively rare, because it requires complete posterior cruciate laxity. It occurs when the lateral tibial plateau subluxes posteriorly on the femur, with the axis shifting posteriorly and medially to the medial joint area. With a hyperextension test, this posterior displacement is obvious and has been labeled as the external rotation recurvatum sign.

Modified Posterolateral Drawer (Loomer's) Test.55,360

The patient lies in the supine position with the hip and knee flexed to 90 degrees, and the lower leg in external rotation (Fig. 20-32).373 If the tibia rotates posteriorly during the test, the test is positive for posterolateral instability, indicating that the following structures may have been injured:

• PCL
• Arcuate–popliteus complex
• LCL
• Posterolateral capsule

The one-plane medial and lateral stability tests, described earlier, can be used to further differentiate which lateral and posterolateral structures are affected.

Dial Test

This test is used to assess abnormal external tibial rotation to help differentiate between an isolated posterolateral corner injury and combined ACL/PCL injuries. The patient lies in the supine position with the knee flexed to 30 degrees over the edge of the table.374 The clinician applies an external rotation force to the patient foot by placing the fingers and thumb alongside the talocalcaneal bone contours (Fig. 20-33). The foot–thigh angle is measured and compared with the uninjured knee. The test is then performed with 90 degrees of knee flexion and the foot–thigh angle is remeasured. When comparing the two angles, a difference of 10 degrees or more is significant. As the knee is flexed to 90 degrees, a reduction in increased rotation may occur although the amount of motion remains greater than the uninjured side if the PCL is still intact. This increased rotation occurs because the PCL is a secondary stabilizer to external rotation and gains mechanical advantage when the knee is flexed.375

Posteromedial Displacement with Valgus Stress Test

The patient lies in the supine position, with the involved leg slightly flexed.373 The clinician pushes the lower leg posteriorly into hyperextension while applying a valgus stress (Fig. 20-34). If the tibia sags posteriorly during the test, the test is positive for posteromedial instability, indicating that the following structures may have been injured:

• PCL
• Posterior oblique ligament
• MCL
• Posteromedial capsule
• ACL

The one-plane medial and lateral stability tests, described earlier, can be used to further differentiate which medial and posteromedial structures are affected.

Anterolateral Rotary Instability

The pathology for this condition almost certainly involves the ACL and, clinically, the instability allows the medial tibial condyle to sublux posteriorly, because the axis of motion has moved to the lateral joint compartment.159

The diagnosis of anterolateral instability is based on the demonstration of a forward subluxation of the lateral tibial plateau as the knee approaches extension and the spontaneous reduction of the subluxation during flexion, in the lateral pivot-shift test.159 This form of instability usually occurs when the individual is either decelerating or changing direction, and the sudden shift of the lateral compartment is experienced as a “giving way” phenomenon, often associated with pain.159

Pivot-Shift Test

This test was first described by Galway et al.376 in 1972 and has been described since by a number of authors.377–380

The pivot shift is the anterior subluxation of the lateral tibial plateau that occurs when the lower leg is stabilized in (almost) full extension, whereby further flexion produces a palpable spring-like reduction.381 The pivot shift is the most widely recognized dynamic instability of the knee, and it has been shown to correlate with reduced sports activity,382 degeneration of the cartilage,383,384 reinjury, meniscal damage,385 joint arthritis,385 and a history of instability symptoms.357,386

Since the majority of patients with an ACL rupture complain of a “giving way” sensation, the pivot-shift test is regarded in current literature as capable of identifying rotational instability.377,378,380

The patient lies in the supine position with the clinician standing to the side of the patient's involved knee. There are two main types of clinical tests to determine the presence of the pivot shift: the reduction test and the subluxation test.

• Reduction test. The clinician stabilizes the patient's lower leg and flexes the knee to 90 degrees with one hand while using the palm of the other hand to medially rotate the tibia, effectively subluxing the lateral tibial plateau (Fig. 20-35).386 A sudden reduction of the anteriorly subluxed lateral tibial plateau is seen as the pivot shift.376
• Subluxation test. This test is effectively the reverse of the reduction test.55 The test begins with patient's knees flexed. The clinician internally rotates the patient's tibias with one hand and applies a valgus stress to the knee joint with the other hand (Fig. 20-36). The clinician slowly extends the knee, maintaining rotation of the tibia. As the patient's knee reaches full extension, the tibial plateau will be felt to relocate. However, only 35–75% of patients whose knees pivot while the patient is under anesthesia will experience such a pivot when awake.355,387–389

Although the specificity of the pivot shift test is very high, namely 98% (95% CI, 25–38), there is little agreement in the literature with regard to the sensitivity of the test, which varies between 0% and 98%.355,364,390 However, in a meta-analysis that looked at 28 studies to assess the accuracy of clinical tests for diagnosing ACL ruptures, Benjaminse et al.391 found the pivot shift test to be very specific both in acute as well as in chronic conditions, and recommended that both the Lachman and pivot-shift tests be performed in all cases of suspected ACL injury.

It is worth noting that the pivot-shift test can be positive with an isolated ACL injury355,392 or a tear or stretching of the lateral capsule,379,393 although an injury to the MCL reduces the likelihood of a pivot shift even with ACL injury.355,394

Patellar Stability Tests

Patellar stability is assessed by gently pushing the patella medially and laterally while the knee is in a position of 90 degrees of flexion. This position is used because it places all of the retinacula on stretch. If this test is positive for laxity, further testing is performed by applying medial and lateral patellar glides, tilts, and rotations, with the knee in relaxed extension, and noting any limitations of motion or excessive excursion (Table 20-8).266

• Glide. The glide component determines the amount of lateral deviation of the patella in the frontal plane. A 5-mm lateral displacement of the patella causes a 50% decrease in VMO tension.395 In the normal knee when fully extended and relaxed, the patella can be passively displaced medially and laterally approximately 1 cm in each direction, or approximately one-third of the width of the patella.187 Displacement of more than half the patella over the medial or lateral aspect is considered abnormal.9 If the patient is apprehensive as the glide maneuver is being performed, the problem is likely to be one of poor patellar engagement. A decreased medial glide of the patella has been found to be related to ITB and/or lateral retinaculum tightness.131
• Tilt. The degree of patellar tilt is assessed by comparing the height of the medial patellar border with the height of the lateral border, which helps to determine the degree of tightness in the deep retinacular fibers. A slight lateral tilt of the patella is normal. An increased medial tilt results from a tight lateral retinaculum. If the passive lateral structures are too tight, the patella will tilt so that the medial border is higher than the lateral border (lateral tilt), making the posterior edge of the lateral border difficult to palpate.266 A posterior tilt results in fat pad irritation.
• Rotation. The rotation component determines whether there is any deviation of the long axis of the patella from the long axis of the femur. If the inferior pole is sitting lateral to the long axis of the femur, the patient has an externally rotated patella, whereas if the inferior pole is sitting medial to the long axis, the patient has an internally rotated patella.

If the patient has one or more of these components present, the clinician needs to determine which of them, if any, is abnormal.

Meniscal Lesion Tests

Mcmurray's Test

The McMurray test was originally developed to diagnose posterior horn lesions of the medial meniscus. The patient lies in the supine position, and the clinician, standing on the same side as the involved knee, maximally flexes the hip and knee. This is accomplished by grasping the patient's foot in such a way that the thumb is lateral, the index and middle fingers are medial, and the ring and little fingers hold the medial edge of the foot (Fig. 20-37). The thumb of one hand is placed against the lateral aspect of the patient's knee (see Fig. 20-37). To test the medial meniscus, the clinician rotates the tibia into external rotation, then slowly extends the knee. To test the lateral meniscus, the clinician flexes the knee again but now internally rotates the patient's tibia and then slowly extends the knee. A positive test traditionally is indicated by an audible or palpable thud or click. In a study by Dervin et al.396 to determine clinicians' accuracy and reliability for the clinical diagnosis of unstable meniscus tears in patients with symptomatic OA of the knee, a positive McMurray test was the only positive predictor of an unstable meniscal tear.396

Numerous variations exist for the McMurray test, including the addition of varus/valgus stresses. An examination of the variation seemed to indicate that the McMurray test has some value as a specific test where a positive test would rule in the disease.

Apley's Test397

The patient is placed in the prone position, with the knee flexed to 90 degrees. The patient's thigh is stabilized by the clinician's knee. The clinician grasps the patient's foot with one hand, distracts the tibia, and rotates the tibia internally and externally, noting whether or not pain is reproduced. A positive test is indicated by worse pain with rotation and is indicative of a rotation sprain of soft tissue. The clinician then applies internal and external rotation with compression to the lower leg, noting any pain and the quality of motion (Fig. 20-38). A positive test for a meniscus tear is indicated by more pain in compression than distraction. It would appear from a number of studies that the Apley test can be used as a specific test to rule in a meniscus tear when positive.

Steinmann's Sign274

Steinmann's test can be used to diagnose meniscal lesions. The patient is placed in the supine position, while the clinician stands to the side. Using one hand, the clinician grasps the patient's lower leg just proximal to the malleolus. The other hand grasps the lateral side of the patient's lower leg as proximal to the knee as possible while also palpating the medial joint space with the fingers (Fig. 20-39). The knee is extended, and the joint line between the patellar tendon and the MCL is palpated. After the painful site is located with the fingers, pressure against this site is maintained while the knee is flexed. After several degrees of motion, the pain disappears, and the painful site can sometimes again be palpated more posteriorly in the joint space. If the most painful site is found in the joint space at the level of the MCL, the test is less reliable, because both the medial meniscus and the ligament move posteriorly during flexion.

Anderson Mediolateral Grind Test

The Anderson mediolateral grind test398 can be used to detect meniscal lesions. The patient is placed in the supine position, and the clinician grasps the involved leg between the trunk and arm. The clinician places the index finger and thumb of the other hand over the anterior knee joint line. With the patient's knee flexed at 45 degrees, a valgus stress is applied as the knee is simultaneously slightly flexed (Fig. 20-40), followed by a varus component while the knee is extended, producing a circular motion of the knee. The maneuver is repeated, increasing the valgus and varus stresses with each rotation.

In one study398 that examined 100 knees with the Anderson mediolateral grind test, as well as arthroscopy, the test was found to have a sensitivity of 70% and a specificity of 67%. However further research needs to be performed to corroborate the statistics reported in this study.

Bounce Home Test

The patient is placed in the supine position and the clinician extends the involved knee to end range (Fig. 20-41). A positive test for meniscus tear is indicated by a block preventing full extension, or pain at end-range extension. A number of studies seem to indicate that neither pain at full extension nor an extension block seem to indicate a torn meniscus.399–401

Figure-4 Test

This test was developed to detect popliteomeniscal fascicle tears, which create instability of the lateral meniscus. The patient lies in the supine position and is asked to place the foot of the involved knee by the contralateral knee, forming a figure 4 (Fig. 20-42). The clinician pushes the involved knee toward the bed. A positive test is indicated by pain over the lateral joint line at the popliteal hiatus. In a very small study402 involving only six patients the test demonstrated a sensitivity of 100%. Further research is necessary before diagnostic conclusions can be made from this test.

Payr Sign

The patient is placed in the supine position or sits and places the foot of the involved knee on the medial aspect of the contralateral knee, forming a figure 4. The clinician pushes the involved knee toward the floor (Fig. 20-43). A positive test for a posterior horn lesion of the medial meniscus is indicated by reproduction of the patient's pain over the medial joint line. In a study by Jerosch and Riemer403 this test was found to have a sensitivity of 54% and a specificity of 44%, demonstrating a diagnostic value similar to that of a coin toss.

Other Special Tests

The remaining special tests for the knee joint complex are dependent on the clinician's needs, the structure of each joint, and the subjective complaints (Table 20-9). These tests are only performed if there is some indication that they would by helpful in arriving at a diagnosis. The special tests help confirm or implicate a particular structure and may also provide information as to the degree of tissue damage.