ACUTE DISLOCATION OF THE PATELLA - MR FINDINGS

PURPOSE: The authors describe magnetic resonance (MR) imaging findings of acute traumatic dislocation of the patella. MATERIALS AND METHODS: MR imaging at 0.1 T was performed in 25 patients with an acute patell ar dislocation, 24 of whom underwent surgery. All patients were young male conscripts, aged 18-22 years. RESULTS: Signal intensity abnormali ties of bone, seen as areas of decreased signal intensity on T1-weight ed images, were found in all 25 patients (100%). The lateral femoral c ondyle was involved in all cases. Signal intensity changes also appear ed in the patella in eight patients and in the lateral tibial plateau in three. Osteochondral fragments seen at plain radiography and cartil age fissuring noted at arthroscopy were not visible at MR imaging. Inj ury of the medial patellar retinaculum was seen at MR in each case. Al l patients had a joint effusion. Lateral subluxation of the patella wa s a common finding. CONCLUSION: Constant findings at MR imaging were ( a) contusion of the lateral femoral condyle, (b) tear of the medial re tinaculum, and (c) joint effusion.