One of the most common injuries of the knee is an anterior cruciate ligament (ACL) tear. There are approximately 200,000 ACL injuries a year in the United States. These injuries often occur when athletes change directions, abruptly stop or plant, or land from a jump. The ACL acts as a stabilizer in the knee and is attached to the femur (thigh bone) to the tibia (shin bone). Its function is to keep the knee from over rotating and prevent the tibia from sliding forward on the femur.

The meniscus is a strong tissue in the knee that provides both cushioning and support. The two menisci (plural of meniscus) of each knee are crescent-shaped wedges that fill the gap between the tibia (shin bone) and femur (thigh bone). The menisci provide joint stability by creating a cup for the femur to sit in. The outer edges are fairly thick while the inner surfaces are thin to accommodate the rounded surface of the femur. If the menisci were missing, the curved femur would be in direct contact with the flat tibia, causing significant pressure, abrasions and wear on the joint.

Patellar (knee cap) dislocation is when the patella moves off to the side of the knee. Individuals typically experience this injury when the foot is planted and a rapid change of direction (twisting) occurs or when a sharp blow to the knee or fall occurs. When a dislocation happens, it can cause extreme pain, stiffness and swelling. A dislocated patella is quite common, especially in younger athletes. However, in some patients, due to abnormalities in their knee anatomy, dislocation can occur with relatively little force and may happen repeatedly.

Articular cartilage is the shiny, white surface that covers the ends of most bones. Articular cartilage protects the ends of bones and allows the joints to glide smoothly with less friction. It also helps to spread the loads applied to a joint. This covering is only a few millimeters thick and it has no blood supply to make the healing process possible. Therefore, if it gets damaged, there is very little capacity for healing.