Dorsal defect of the patella with cartilage involvement and bone marrow edema

Case contributed by Henry Knipe
Diagnosis almost certain

Presentation

Knee pain post fall. Suspected ACL injury.

Patient Data

Age: 13 years
Gender: Female

No knee joint effusion. 

No acute meniscal tear. No cruciate or collateral ligament injury. Intact extensor mechanism.

Superolateral patellar chondral defect with subchondral geode with sclerotic rim and mild adjacent bone marrow edema. Unremarkable patellofemoral morphology. Normal patellar height.

Medial and lateral tibiofemoral compartment articular cartilage is intact.

Tiny simple bone cyst distal femur.

Case Discussion

This is a variant or atypical dorsal defect of the patella, which is thought to be a developmental anomaly related to delayed ossification. Classic teaching is that these are not associated with bone marrow edema and the overlying cartilage is intact, although more recent literature 1 has demonstrated these changes. 

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