Large lipohaemarthrosis. Avulsion fracture of the medial patellofemoral ligament. Lateral patellar retinaculum is intact. Patella is not dislocated but is laterally subluxed. Bone marrow oedema 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.