Acute dislocation of the patella is a common injury in adolescents and adults and occurs most commonly during sports participation. The injury is most commonly an indirect injury occurring with a pivoting away from the involved knee. Risk factors include young age, generalized laxity, patella alta, patellar subluxation, and trochlea or patellae dysplasia.

The essential lesion of the lateral patellar dislocation is a tear of the medial patellofemoral ligament coursing from the medial patella to the medial epicondyle. The medial patellofemoral ligament is superficial to synovium and the femoral attachment lies posterior to the medial synovial reflexion and is not seen at arthroscopy. The retinaculum becomes confluent with the medial patellofemoral ligament distally. There are frequently bone fragments detached from the medial patella and lateral femoral condyle at the lateral margin and just anterior to the terminal sulcus. Patellar subluxation with an increased TT-TG distance is common.

Studies applied to an entire group of dislocations have not shown acute surgery to be of great benefit. Conservative treatment is usually recommended. I made an exception in the case of large patellar chondral injuries with significant subluxation. Removal of loose bodies, lateral retinacular release and medial patellofemoral ligament repair or reconstructon with a hamstring graft are then recommended.

In cases of recurrent dislocation I recommend an Elmslie-Trillat procedure in addition when there is significant subluxation and closed physes.