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.
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.
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.
Bone, ligaments, and menisci in the knee. (A) Anterior view. (B) Posterior view. (From Saladin, KS: Anatomy and physiology, ed. 5, Dubuque, IA: McGraw-Hill Higher Education, 2010.)
Muscles and ligaments provide the main source of stability in the knee.
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.
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 ...