Acute lateral patellar dislocation can occur as a result of knee trauma and is most often seen in young athletes. The dislocation often reduces spontaneously without treatment, and the patient may not be aware that it has occurred. After such an event, the clinical examination is nonspecific, and as many as 75% of patients are misdiagnosed on initial physical exam and radiographs . MR has been useful for diagnosis as several specific findings have been described. These include hemarthrosis/effusion, lateral femoral condyle and medial patellar facet bone contusions, osteochondral injury, and medial retinacular injury. The medial patello-femoral ligament, which has been identified as the major
restraint to lateral dislocation of the patella, is often injured when patellar dislocation occurs (Fig. 9) .
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