Posterolateral Knee
This prospective study was based upon recent descriptions of specific anatomic components of the posterolateral knee. Its purpose was to contrast the magnetic resonance imaging (MRI) appearance of the normal individual anatomic components of the posterolateral knee with the MRI appearance of injured structures, and to assess the accuracy of the use of MRI in the identification of specific structures within the posterolateral corner of the knee. A specific MRI protocol was developed for identification of posterolateral knee structures which included thin slice coronal oblique T1-weighted images through the entire fibular head. MR imaging of seven normal knees allowed for consistent identification of the following structures of the posterolateral knee: iliotibial band (superficial and deep layers), long head biceps femoris (direct and anterior arms), short head biceps femoris (direct and anterior arms), popliteus complex (popliteus tendon and popliteofibular ligament), mid- third lateral capsular ligament (meniscofemoral and meniscotibial ligament components), fibular collateral ligament, lateral gastrocnemius tendon, and the fabellofibular ligament. The MRI appearance of corresponding grade III injured structures was identified prospectively in twenty patients and verified at the time of surgical reconstruction. The sensitivity, specificity, and accuracy of the most frequently injured posterolateral knee structures in this series were as follows: iliotibial band-deep layer (91.7%, 100%, and 95%); short head biceps femoris-direct arm (81.3%, 100%, and 85%); short head biceps femoris-anterior arm (80%, 100%, and 85%); mid-third 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 (78.6%, 66.7%, and 75%); and the fabellofibular ligament (92.3%, 85.7%, and 90%). Normal structures of the posterolateral corner of the knee were consistently identified on MRI sections through the knee. MRI of the knee using this specific adapted protocol was useful in the identification of tears of specific ligamentous, tendinous, and aponeurotic structures in patients with grade 3 injuries to the posterolateral corner of the knee. In complex cases where posterolateral knee complex injures are suspected, MRI is extremely useful in the identification of injuries to specific individual structures of the posterolateral knee.
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