Presentation
Knee pain after instability.
Patient Data
Large knee joint effusion.
Menisci are intact. Anterior and posterior cruciate ligaments are intact. Medial and lateral collateral ligaments are intact. Partial tear of the popliteus tendon insertion measuring 0.5 cm. Posterolateral corner structures otherwise appear uninjured.
Insall-Salvati ratio 1.4, within normal limits. Trochlear dysplasia with a shallow groove and small medial trochlear facet superiorly. TT-TG distance is increased at 25 mm. Lateral patellar subluxation without dislocation.
Marrow edema and cortical disruption through the medial aspect of the patella involving the medial patellofemoral ligament and medial patellar retinacular attachments. Proximally, the medial patellofemoral ligament is not redundant suggesting partial injury. Peripheral medial patellar facet cartilage is injured. Lateral femoral trochlear cartilage fissuring.
Microtrabecular injury to the non-weight-bearing lateral femoral condyle. Articular cartilage of the medial and lateral tibiofemoral compartments are preserved.
Case Discussion
Transient lateral patellar dislocation with a cortical avulsion injury involving the medial patellofemoral ligament and medial patellar retinaculum and corresponding microtrabecular injury to the non-weight-bearing lateral femoral condyle.
Background predisposing factors of trochlear facet asymmetry, shallow trochlear groove and tibial tuberosity lateralization are present.
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