Osteoarthritic knee joint, illustration. This view shows the destruction of cartilage on the articular surfaces of the femur (the thigh bone). Erosion of the cartilage leads to a loss of joint space and progressive deformity. Arthritic changes in the knee commonly occur with increasing age, causing much pain and crippling disability. Here, the cartilage of the lateral (left) and medial condyles (articular surfaces) appears chipped and eroded. Also featured are the quadriceps femoris muscle (top) and the anterior cruciate ligament (positioned vertically between the two condyles). The knee is one of the most common sites of osteoarthritis. Shown here are marginal osteophytes, degenerated menisci, and destruction of articular cartilage.