Medial patellofemoral ligament avulsion injury at the patella: classification and clinical outcome.

Abstract

To define medial patellofemoral ligament (MPFL) injury characteristics at the patellar attachment and clinical outcome in patients with primary traumatic patellar dislocation and MPFL avulsion injury at the patella. Magnetic resonance imaging (MRI) was used to assess patients with primary (first-time) patellar dislocation and MPFL injury at the medial margin of the patella. Fifty-six patients with patellar attachment MPFL injury were enrolled in the study. Thirteen patients underwent surgical fixation of the avulsed MPFL and patellar medial margin osteochondral fracture, and the remaining patellar MPFL injures were treated nonoperatively. Forty-four patients were evaluated clinically at median four (range 1-10) years after patellar dislocation. The follow-up included evaluation of recurrent patellar instability, subjective symptoms, and functional limitations. Three types of patellar MPFL injuries were found; type P0 with ligamentous disruption at the patellar attachment, type P1 with bony avulsion fracture from the medial margin of the patella, and type P2 with bony avulsion involving articular cartilage from the medial facet of the patella. Of the patellar MPFL avulsion injuries that underwent initial surgical fixation, two patients (2/13) reported an unstable patella at follow-up. Fifty-five per cent (17/31) of patellar MPFL avulsion injuries that were treated nonoperatively had recurrent patellar instability (n.s.). The median Kujala score was 90 for patellar avulsion with surgical fixation and 86 for patellar avulsion without surgical fixation (n.s.). Patellar attachment MPFL injury showed three different patterns, classified as types P0, P1, and P2. MRI can be used to assess the injury pattern. Patellar MPFL avulsion injuries do not benefit from acute surgical repair compared with nonsurgical treatment. Type P2 patellar MPFL avulsion includes an osteochondral fracture that may require surgical fixation. Prognostic study, Level III.