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Patellar Instability / Patellar Subluxation


The patella, or kneecap, rides along a trough or groove at the end of the thighbone (femur), much like a bobsled down a track. The patella is attached to the strong thigh muscles on one end, and is attached via the patellar tendon to the front of the shinbone (tibia) on the other end. Thus, when the thigh muscles contract, they pull on the patella, and the leg straightens. The patella is supposed to ride in the center of its track. With abnormal patellar tracking, the kneecap can start to ride out of its groove, and can even dislocate.


Common Causes

Twisting injury to the knee, a direct blow to the kneecap. Certain people have a predisposition to this problem, based on their own knee alignment.



Pain in the front of the knee, increased with exercise or activity. A patellar dislocation results in an obvious deformity of the front of the knee, with an inability to move the knee.


Physical Findings

Abnormal patellar tracking on physical examination. Tenderness with compression of the patella, or with attempts to shift the patella to the side.



History examination, and x-rays. Special x-rays can detail how the patella tracks down the end of the thighbone.


Non-operative Treatment

Physical therapy, with attention directed on strengthening specific muscle groups. Anti-inflammatory medication is helpful to reduce discomfort. Patellar stabilizing knee braces are effective.


Surgical Treatment

Patellar realignment procedures. These range from an arthroscopic lateral release, to open realignment of the insertion of the patellar tendon on the tibia.


Injury Comment

The majority of cases can be successfully treated with therapy and exercise. Symptoms may be exacerbated during growth spurts in adolescents.