Presentation
Recurrent patellar dislocations. Patellar tendon avulsion repair 3 years ago.
Patient Data
Wiberg type III patella is noted with very shallow trochlear groove (likely to be the underlying cause of recurrent patellar dislocations).
Cortical irregularity, high signal changes and some ligamentous thickening can be seen at the level of the medial patellofemoral ligament insertion in keeping with an MPFL tear.
There is no evidence of meniscal injury apart from an incomplete tiny radial tear through the body of the lateral meniscus. On coronal images, the lateral meniscal body width of 17 mm suggests incomplete discoid meniscus (more prone to injuries).
The modified Insall-Salvati ratio (last image) measures 75 mm / 34 mm = 2.2 (blue / yellow) in keeping with patella alta. Appropriate measurements can be made in 30° flexion of the knee joint.
Case Discussion
Look for predisposing factors (patellar morphology, trochlear grove) and possible complications (osteochondral fracture, MPFL tear) of lateral patellar dislocations.
Patellar position can be accurately measured in 30° flexion of the knee joint.
Small tears are not unusual with the background of discoid meniscus.
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