MR imaging of patellar retinacular ligament injuries.

Seventeen patients with patellar retinacular ligament injuries were evaluated with magnetic resonance (MR) imaging. MR findings were correlated with clinical, surgical, and arthroscopic findings. The injuries involved the medial retinacular ligament in 16 of 17 patients and the medial and lateral retinacular ligament in one patient. Nine of 17 patients showed MR evidence of a patellar dislocation. In these patients, a triad of findings that included focal impaction injuries involving the lateral femoral condyle, osteochondral injuries of the medial patellar facet, and injuries of the medial retinacular ligament were seen. Seven of the nine patients with patellar dislocation injuries had frank osteochondral injuries. The injured retinaculum had an indistinct, irregular appearance associated with edema and hemorrhage. The patellar dislocations were clinically unsuspected in the initial evaluation of eight of these nine patients. In eight of 17 patients, the mechanism of injury was a patellar tendon tear (n = 1) or valgus hyperextension (n = 7). In the seven patients with hyperextension injuries, three had associated meniscal and cruciate ligament tears. MR imaging can help define patellar retinacular and associated osteochondral injuries, which may be clinically useful information.