Patellar instability means that the kneecap is not sitting well into its groove on the lower end of the thigh bone or the femur. The patella tends to ride on the outer aspect of the groove and causes pain and swelling. These patients may have damage to the cartilage. Occasionally the patient may have frank episodes of instability when the kneecap dislocates to the outside of the groove, will present with acute onset of pain and swelling.
The kneecap can be reduced back but the patient may have had injury to the cartilage as well as the ligament on the inner side of the knee. Some patients may have inherited factors that may cause patellar instability. If the patient has recurrent instability or damage to the cartilage and ligament, then these patients may need surgery to improve their function as well as prevent long-term effects of patellar instability.