After completion of this chapter, the physical therapist should be able to do the following:
Describe the functional biomechanics associated with normal function of the knee.
Utilize a general rehabilitation progression when treating knee injuries.
Integrate a comprehensive understanding of pathomechanics and mechanism of injury into the rehabilitation of ligamentous and meniscal injuries.
Integrate a comprehensive understanding of pathomechanics and mechanism of injury into the rehabilitation of patellofemoral and extensor mechanism injuries.
Justify the use of external supports to augment the rehabilitation process.
Implement a functional progression to ensure safe return to activity.
FUNCTIONAL BIOMECHANICS OF THE KNEE
The study of biomechanics, along with functional anatomy, is a cornerstone to knee rehabilitation. A complete understanding of joint articulations, arthrokinematics, and the structures responsible for accepting joint loads and controlling movement is essential for the clinician to make sound decisions in the diagnosis and treatment of musculoskeletal disorders. Despite the relative simplicity of a hinge-type joint, the knee provides an interesting biomechanical study because of the intricacies required to maintain stability without good bony support along with attenuating forces greater than four times the weight of the body. The patellofemoral joint and the pain syndromes often associated with the knee also present a challenge when diagnosing pathology or devising a rehabilitation program.
Tibiofemoral Articulation: Menisci-Femoral Condyles
The condyles of the distal femur articulate with the shallow, concave tibial plateau, resulting in significant tibiofemoral joint incongruency. Tibiofemoral stability would be insufficient if left solely to the skeletal structure. The medial and lateral menisci provide additional congruency to the joint through their semicircular shape and peripheral thickness, thus forming a wedge surrounding the femoral condyles. Therefore, the menisci have been shown to provide increased joint conformity at the tibiofemoral joint and share the compressive forces applied to the joint surface.
The contact area of the menisci varies significantly during knee range of motion (ROM). In weight bearing, the total contact area of the menisci decreases with knee flexion. Although mean surface area increases in non-weightbearing conditions, total menisci contact area also decreases during knee flexion. Following a meniscectomy, surface contact area decreases, resulting in a greater amount of stress upon the contact surface. Maquet and colleagues injected contrast material into cadaver joints to examine contact area in knee joints during compressive loads. When the knee is brought from extension to flexion, there is a posterior translation of the medial and lateral contact areas along with a decrease in contact surface area with knee flexion.1
The ability of the tibiofemoral joint to withstand forces imposed by the superincumbent weight of the body combined with the ground reaction force transmitted through the distal extremity requires interaction of multiple structural factors. The longitudinal axis of the femur extends laterally ...