Knee

About the Knee

The knee is the largest joint in the body and one of the most complex. It is formed by the femur, the tibia, and the patella, or kneecap, which sits in the tendon of the quadriceps muscle and improves its leverage. It functions mainly as a hinge, allowing flexion and extension, with a small amount of rotation when bent. Two C shaped cartilage pads, the medial and lateral menisci, cushion and stabilize the joint between the femur and tibia. Stability comes largely from ligaments: the anterior and posterior cruciate ligaments inside the joint prevent the tibia from sliding forward or backward, while the medial and lateral collateral ligaments resist sideways forces. The whole joint is enclosed in a capsule lined with synovial membrane, and several fluid filled bursae reduce friction around it. Because it bears so much load, the knee is a frequent site of sports injuries such as ACL and meniscus tears and of osteoarthritis, and total knee replacement is one of the most common joint replacement procedures.