Transient lateral patellar dislocation
Knee pain post trauma.
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Large joint effusion. Circumferential subcutaneous tissue fluid around the knee joint.
The anterior horn of the medial meniscus is nearly completely extruded with avulsion of the root attachment of the anterior horn. Peripheral vertically oriented tear of the anterior horn of the lateral meniscus with hyperintensity of the posterolateral meniscocapsular ligaments and a likely horizontal peripheral tear of the body/posterior horn junction of the lateral meniscus.
The medial collateral ligament is intact. Hyperintensity around the proximal lateral collateral ligament at its femoral attachment in keeping with a low-grade sprain injury.
The cruciate ligaments are intact.
Partial width, partial thickness tear of the anterior fibers of the distal quadriceps tendon. Patellar tendon is intact.
There is a full thickness chondral defect of the median patellar pole and lateral patellar facet. Femoral trochlear cartilage is intact. Bone marrow edema through the medial aspect of the patella extending to the inferior pole with an avulsion injury of the medial patellar retinaculum and medial patellofemoral ligament. There is an osteochondral impaction fracture of the lateral aspect of the lateral femoral condyle. Articular cartilage within the tibiofemoral compartment is otherwise preserved.
Within the medial aspect of the suprapatellar recess is an intra-articular body, which is likely cartilaginous in origin, measuring up to 11mm.
The pattern of bone contusion in knee injuries is very helpful in determining the mechanism and thus the expected injuries. This is the typical pattern of transient lateral patellar dislocation with many associated soft tissue injuries.