Patellofemoral osteoarthritis after patellar dislocation.

Clinical and radiographic studies were done for 85 patients treated conservatively for acute primary patellar dislocation occurring an average 13 years (range, 6-26 years) previously. Osteoarthritic changes in the patellofemoral joint were evaluated with special reference to the primary conservative treatment and treatment of redislocations (operative or conservative) or treatment for other subsequent problems such as pain and/or subluxations (late surgery). The patients were divided into two groups on the basis of findings in the unaffected knee and other joints. There were 56 patients (66%) with predisposing factors such as an abnormal quadriceps angle, positive apprehension test, quadriceps muscle atrophy, or generalized joint laxity common to all patients. Patients with or without predisposing factors did not differ from each other in terms of arthritic changes. Patellofemoral joint degeneration was found in the affected knee in 19 patients (22%) and in the unaffected knee in nine (11%). Conservative treatment without subsequent redislocations resulted in osteoarthritic changes in 29% of the cases and in 13% of cases with occasional redislocations. Osteoarthritic changes were found in 17% of patients treated operatively and in 12% of patients treated conservatively for redislocations. Of the patients who underwent late surgery for patellofemoral pain or subluxations, 35% showed osteoarthritic changes. In general, there were more degenerative changes in patients with stable patellae (no redislocations) than in those with occasional recurrences, especially in older and heavier patients.