Lateral patellar dislocation is usually associated with disruptive changes to the medial patellar stabilizers (retinaculum and medial patello-femoral ligament). Patellar dislocation most commonly results from a twisting motion, with the knee in flexion and the femur rotating internally on a fixed foot (valgus-flexion-external rotation). May be associated with avulsion fracture  of the medial patellar facet as in this case.

MRI is superior in evaluation of ligament and retinaculum as well as bone marrow changes.