Patellar sleeve avulsion

Case contributed by Dr Henry Knipe

Presentation

Acute injury. Unable to straighten leg.

Patient Data

Age: 13 years
Gender: Male
mri

Small knee joint effusion. 

No meniscal tear. Cruciate and collateral ligaments are intact. 

The quadriceps tendon is intact. Proximal patellar tendon high signal and swelling. Adjacent fluid and edema of the anterosuperior Hoffa's fat pad. Inferior patellar pole bone marrow and subperiosteal edema; possible avulsion fracture at the inferior pole. Prominent inferior patellar pole edema with no chondral injury identified. Articular cartilage of the patellofemoral compartment is preserved. Patellar height is normal.

At the distal femoral metaphysis posteromedially there is subperiosteal edema with a high signal of the medial gastrocnemius insertion. 

Case Discussion

Patellar sleeve fractures are rare pediatric injuries of the extensor mechanism, they most often are indirect from forceful eccentric contraction, e.g. during jumping. 

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