Acute-on-chronic transient lateral patellar dislocation with trochlear dysplasia
Presentation
Episode of knee instability.
Patient Data
Patellar height is normal. Lateral patellar tilt and lateralization of the patella. At 3 cm above the joint line, there is trochlear dysplasia characterized by a small medial facet and a shallow trochlear groove as well as a shallow lateral trochlear inclination angle. TT-TG distance is increased at 22 mm.
Bone contusions of the medial aspect of the patella and lateral femoral condyle. At the medial patella is a 6 mm ossicle with edema of the insertional fibers of the medial patellofemoral ligament, which generally appears thickened but without redundancy to suggest a full-thickness tear.
Case Discussion
This is a case of acute on chronic transient lateral patellar dislocation with an ossicle at the medial patella in keeping with a chronic medial patellofemoral ligament avulsion injury with ligamentous edema suggesting a recurrent partial tear. This occurs on a background of patellar maltracking consisting of trochlear dysplasia with patellar lateralization and lateral patellar tilt, as well as moderate chondromalacia patellae.
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