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Chapter 16: The Knee and Related Structures

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©Courtesy Wayne Clausen Jr.

OBJECTIVES

When you finish this chapter you will be able to:

  • Describe the anatomical relationships of the bones, ligaments, and muscles that surround the knee joint.

  • Explain how to prevent knee injuries.

  • Briefly describe how to assess an injury of the knee joint.

  • Recognize injuries to the stabilizing structures of the knee.

  • Differentiate between acute and overuse injuries that occur at the knee joint.

  • Identify injuries that can occur to the patella.

  • Describe injuries that can occur to the extensor mechanism.

INTRODUCTION

The knee is considered one of the most complex joints in the human body. Because so many sports place extreme stress on the knee, it is also one of the most frequently injured joints. The knee is commonly considered a hinge joint because its two principal movements are flexion and extension. However, because rotation of the tibia is an essential component of knee movement, the knee is not a true hinge joint. The stability of the knee joint depends primarily on the ligaments, the joint capsule, and the muscles that surround the joint. The knee functions to provide stability in weight bearing and mobility in locomotion.

KNEE ANATOMY

Bones

The knee joint consists of four bones: the femur, the tibia, the fibula, and the patella (Figure 16–1). These four bones form several articulations between the femur and the tibia, the femur and the patella, the femur and the fibula, and the tibia and fibula. The articular surfaces of the knee joint are completely enveloped by the largest joint capsule in the body. Synovial membrane lines the inner surface of the joint capsule.

Muscles and ligaments provide the main source of stability in the knee.

FIGURE 16–1

Bone, ligaments, and menisci in the knee. (A) Anterior view. (B) Posterior view.

An illustration of the anterior and posterior views of the knee joint shows the related structures annotated and categorized into medial and lateral. Anterior view: The femur is the long bone of the thigh. The lateral condyle is the smaller and less prominent of the two projections on the distal end of the femur located on the outer side. The lateral collateral ligament is a thin band of tissue running along the outside of the knee. It connects the femur to the fibula. The lateral meniscus is the thickened crescent-shaped cartilage pad in the outer portion of the joint. The fibula is the long, slender bone located laterally in the lower leg that extends to the ankle. The tibia is the shinbone located medially in the lower leg extending from the knee to the ankle joint. The larger of the two expanded rounded projections at the distal end of the femur is located on the inner side. The posterior cruciate ligament is a fibrous band of tissue on the inside of the knee, connecting the tibia to the femur, forming an "X" pattern that stabilizes the knee against front-to-back and forces. The anterior cruciate ligament is a band of dense connective tissue that crosses from the underside of the femur to the top of the tibia and prevents the tibia from sliding out in front of the femur. The medial meniscus is a C-shaped wedge fibrocartilaginous structure located between the condyle of the femur and tibia on the inner side. The medial collateral ligament is a wide, thick band of tissue that runs down the inner part of the knee from the femur to the tibia about 4 to 6 inches from the knee. The patellar ligament is an extension of the quadriceps tendon. It extends from the patella to the tibial tuberosity. Posterior view: The medial structures labeled are the medial condyle, medial collateral ligament, medial meniscus, and posterior cruciate ligament. The lateral structures labeled are the anterior cruciate ligament, lateral collateral ligament, and lateral meniscus.
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The distal end of the femur expands into the lateral and medial femoral condyles, which are designed to articulate with the tibia and the patella. The patella, or kneecap, is located in the tendon of the quadriceps muscle group on the front of the knee and moves up and down in a groove between the two femoral condyles as the quadriceps muscle group contracts and relaxes. The proximal end of the tibia, or the tibial plateau, is very flat and must articulate with the round condyles of the femur.

Menisci

The medial meniscus and lateral meniscus are fibrocartilage disks that are shaped like bowls, thicker on the outside border and thinner on the inside (Figure 16–2). They lie on top of the flat tibial plateau and function to make the rounded femoral condyles fit better ...

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