[The value of MR tomography in traumatic patella dislocations].

Purpose: To describe the MR imaging findings in patients with lateral patellar dislocation.

Material And Methods: The MRIs of 31 patients with patellar dislocation were evaluated retrospectively. Arthroscopic surgery was performed in 23 cases.

Results: Hemarthrosis was found in 30/31, contusions of the lateral femoral condyle in 30/31 and of the medial patellar facet in 26/31 cases. Injury of the medial patellar retinaculum was seen in 28/31 cases. Osteochondral fractures were found in 18 patients; compared to arthroscopy there were one false-positive and 5 false-negative findings concerning loose cartilage bodies. In 7 cases, patellar dislocation was not suspected before MR imaging.

Conclusion: Hemarthrosis, lateral femoral and medial patellar contusion, and retinacular disruption are typical findings after lateral patellar dislocation. A careful search for free osteochondral fragments is mandatory as it influences the indication and performance of arthroscopic surgery.