Lateral patellar dislocation with avulsion fracture

Case contributed by Dr Mohamed Saber

Presentation

Knee trauma followed by severe pain and swelling.

Patient Data

Age: 14 years
Gender: Male

The patella is displaced laterally with associated displaced avulsion fracture of the medial patellar facet.

Moderate knee joint effusion and periarticular soft tissue edema are also noted.

Incidental distal medial femoral metadiaphyseal eccentric cortical based lobulated lytic lesion with marginal sclerosis likely non-ossifying fibroma.

Case Discussion

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.

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