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Infrapatellar (Hoffa) fat pad herniation

Case contributed by Yuan Ling
Diagnosis almost certain

Presentation

Mum noticed a painless lump at the anterolateral knee on flexion. No history of trauma or penetrating injury.

Patient Data

Age: 20 months
Gender: Male

Dynamic ultrasound

ultrasound

The palpable lump was examined, revealing a 5 x 3 mm hypoechoic soft tissue mass inferolateral to the patella. This reduced on knee extension, through a 3 mm defect in the lateral patellar retinaculum. Anteriorly, the iliotibial band was intact to Gerdy's tubercle; posteriorly the lateral collateral ligament was intact to the fibular styloid.

Case Discussion

Findings are consistent with infrapatellar fat pad herniation through a defect in the lateral patellar retinaculum.

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