Medial patellofemoral ligament injury. Location-based rate of recurrent patellar dislocation after non-operative treatment.

Objectives: The role of the medial patellofemoral ligament (MPFL) as a patellofemoral joint stabilizing structure is undisputable. After traumatic patellar dislocation, MPFL injury, together with bone edema in the medial patellar facet and lateral femoral condyle, is a pathognomonic finding in magnetic resonance imaging (MRI). MPFL injury in the femoral insertion has been reported to most likely predict recurrent dislocations. The objective of this study was to detect if any MPFL injury location predicts the earliest onset of the patellar re-dislocation.

Methods: In total, 64 eligible patients with a first-time traumatic patellar dislocation were recruited to the trial. The diagnosis was confirmed within 3 weeks with 3T magnetic resonance imaging. The location of the MPFL injury in MRI was localized at the patellar insertion, midsubstance area, femoral insertion, or a combination of these. During the three-year follow-up period, patellar re-dislocations, range of motion, quadriceps muscle atrophy, and daily symptoms were determined. All the patients were treated non-operatively.

Results: Out of 64 patients, 33 (51.6%) had at least one episode of patellar re-dislocation. Re-dislocations occurred in 8 out of 25 (32.0%) patients with the main injury at the femoral insertion, 5 out of 15 (33.3%) patients with the main injury at the midsubstance area, and 10 out of 24 (41.7%) patients with the main injury at the patellar insertion during the 36 months follow-up (p ​= ​0.758). According to Kaplan-Meier analysis, the location of MPFL injury did not have any statistically significant effect on the timing of re-dislocations. At 36 months, survival of patients with MPFL injury at the patellar insertion was 70.8%, which was not statistically significantly different than the survival in patients with injury at the femoral insertion (88.0%) or at the midsubstance area (93.3%). No differences between single and multiple MPFL injuries were found. At 4 weeks, the range of motion was more restricted in patients with MPFL injury at the femoral insertion (93.4° vs. 108.0° for injury at the midsubstance area and 107.7° at the patellar insertion).

Conclusion: The location of MPFL injury did not have any statistically significant effect on timing or the rate of re-dislocations. The MPFL injury at the femoral insertion predicts decreased range of motion (ROM) of the knee and increased quadriceps muscle atrophy during the first three months after sustaining injury.

Level Of Evidence: Level III.