The magnetic resonance imaging appearance of individual structures of the posterolateral knee. A prospective study of normal knees and knees with surgically verified grade III injuries.

The purpose of this study was to contrast the magnetic resonance imaging appearance of uninjured components of the posterolateral knee with that of injured structures, and to assess the accuracy of magnetic resonance imaging in identifying posterolateral knee complex injuries. Thin-slice coronal oblique T1-weighted images through the entire fibular head were used to identify the posterolateral structures in seven uninjured knees. The appearance of corresponding grade III injuries to these structures was identified prospectively in 20 patients and verified at the time of surgical reconstruction. The sensitivity, specificity, and accuracy of imaging for the most frequently injured posterolateral knee structures in this series were as follows: iliotibial band-deep layer (91.7%, 100%, and 95%), short head of the biceps femoris-direct arm (81.3%, 100%, and 85%), short head of the biceps femoris-anterior arm (92.9%, 100%, and 95%), midthird lateral capsular ligament-meniscotibial (93.8%, 100%, and 95%), fibular collateral ligament (94.4%, 100%, and 95%), popliteus origin on femur (93.3%, 80%, and 90%), popliteofibular ligament (68.8%, 66.7%, and 68%), and the fabellofibular ligament (85.7%, 85.7%, and 85.7%). Magnetic resonance imaging of the knee was accurate in the identification of these injuries.