The patella, or knee cap, is an important component of the knee joint. It is a bone through which the tendon of the quadriceps, the largest muscle in the body, inserts onto the front aspect of the top of the tibia (shin bone). The back side of the patella is covered by thick articular cartilage and moves against the end of the femur (thigh bone) which is also covered by thick articular cartilage. The end of the femur has a small groove in which the patella tracks. Some people have a very shallow groove and some have a deeper groove. However, the groove is not enough to maintain the patella’s position. There are important soft tissue attachments that help control the patella’s motion. These can be torn by a traumatic event or stretched over time. Also, some people have soft tissue attachments that are genetically loose or thin and insufficient to keep the patella in its track, especially when exerting.
With patellar instability, one can have episodes of the patella coming partially out of the groove (called patellar subluxation) or completely coming out of the groove (dislocation). These can be very painful and debilitating. Treatment is aimed at restoring the patella’s position and trying to maintain it in its track.
Depending on the cause and severity of the patellar instability, one can control or correct it by either non-operative or operative means. Non-operative means include muscle strengthening exercises, as well as the use of certain braces (see also "Braces" in the "Treatment Modalities" section). Operative correction involves balancing the soft tissue attachments to the patella by surgical releases of overly tight structures and/or tightening of overly loose structures. Also, sometimes the insertion of the quadriceps tendon itself onto the shin bone needs to be altered surgically.
Successful treatment depends on correct diagnosis and intervention by the physician as well as a lot of effort in rehabilitation and compliance with exercises and activity modification by the patient.