A painful disorder of the knee in which the cartilage behind the patella (kneecap) is damaged.
Adolescents are most commonly affected.
The condition may result from knee injuries or sporting activities in which the knee is bent for long periods.
This action weakens the inner part of the quadriceps muscle (at the front of the thigh) causing the patella to tilt when the knee is straightened and rub against the lower end of the femur.
The cartilage that covers both bones becomes roughened, causing pain and tenderness.
Treatment is with analgesic drugs and exercises to strengthen the thigh muscles.
Rarely, surgery may be needed.
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