Avulsion fracture of the medial patellofemoral ligament

Case contributed by Henry Knipe
Diagnosis certain

Presentation

Painful left knee. Trauma.

Patient Data

Age: 12 years
Gender: Female

Large joint effusion. Mild lateral patellar subluxation. Multiple bone fragments are seen at the medial aspect of the patella, in keeping with fracture, possibly involving avulsion of the medial patellar retinaculum. No femoral or tibial fracture identified.

Large lipohemarthrosis. Avulsion fracture of the medial patellofemoral ligament. Lateral patellar retinaculum is intact. Patella is not dislocated but is laterally subluxed. Bone marrow edema at the medial patalla and lateral femoral epiphysis, which is in keeping with a prior lateral patellar dislocation. The patellar tendon is intact. No meniscal tear. Cruciate and lateral collateral ligaments are intact. 

Case Discussion

Medial patellofemoral ligament avulsion injuries are common after lateral patellar dislocation, more common at the patellar insertion (~50%) than the femoral insertion (~25%) 1. The medial patellofemoral ligament is one of the main components of the middle layer of the medial patellar retinaculum, and is one of the major medial patellar stabilizers 2

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