TRANSIENT LATERAL PATELLAR DISLOCATION - DIAGNOSIS WITH MR-IMAGING

OBJECTIVE. Transient lateral patellar dislocation is frequently diffic ult to diagnose accurately on the basis of clinical findings. Accordin gly, we studied the MR findings in 26 cases to determine if MR imaging is useful in establishing the diagnosis. MATERIALS AND METHODS. A ret rospective review of 1450 MR examinations of acutely injured knees was performed to determine the MR findings resulting from transient later al patellar dislocation. A distinctive constellation of MR findings re flecting the known mechanism of injury indicative of transient lateral patellar dislocation was found in 26 patients. Patellar dislocation w as not clinically suspected before imaging in 19 (73%) of these 26 pat ients; most patients had been referred for suspected injury of the cru ciate ligaments or menisci. Axial, sagittal, and coronal MR images wer e obtained in all patients, and all had clinical follow-up. Correlatio n of MR findings with surgical findings was possible in six. RESULTS. Specific components of the constellation of MR findings included disru ption or sprain of the medial retinaculum in 25 (96%) of 26 patients, lateral patellar tilt or subluxation in 24 patients (92%), lateral fem oral condyle contusion in 21 patients (81%), osteochondral injury in 1 5 patients (58%), and joint effusion in all 26 patients (100%). Concom itant injury to major ligaments or menisci was present in eight (31%). CONCLUSION. Our findings suggest that patients with transient lateral patellar subluxation have a distinctive constellation of MR findings that can be used to distinguish this entity from other common knee inj uries.