Lateral patellar dislocation with avulsion fracture
Citation, DOI and case data
Knee trauma followed by severe pain and swelling.
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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.
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.
- Sanders TG, Morrison WB, Singleton BA, Miller MD, Cornum KG. Medial patellofemoral ligament injury following acute transient dislocation of the patella: MR findings with surgical correlation in 14 patients. J Comput Assist Tomogr 2001; 25:957-962.
- Lance E, Deutsch AL, Mink JH. Prior lateral patellar dislocation: MR imaging findings. Radiology 1993; 189:905-907.