The role of the cruciate and posterolateral ligaments in stability of the knee. A biomechanical study.

The role of the posterolateral and cruciate ligaments in restraining knee motion was studied in 11 human cadaveric knees. The posterolateral ligaments sectioned included the lateral collateral and arcuate ligaments, the popliteofibular ligament, and the popliteal tendon attachment to the tibia. Combined sectioning of the anterior cruciate and posterolateral ligaments resulted in maximal increases in primary anterior and posterior translations at 30 degrees of knee flexion. Primary varus, primary internal, and coupled external rotation also increased and were maximal at 30 degrees of knee flexion. Combined sectioning of the posterior cruciate and posterolateral ligaments resulted in increased primary posterior translation, primary varus and external rotation, and coupled external rotation at all angles of knee flexion. Examination of the knee at 30 degrees and 90 degrees of knee flexion can discriminate between combined posterior cruciate ligament and posterolateral injury and isolated posterolateral injury. The standard external rotation test performed at 30 degrees of knee flexion may not be routinely reliable for detecting combined anterior cruciate and posterolateral ligament injury. However, measurements of primary anterior-posterior translation, primary varus rotation, and coupled external rotation may be used to detect combined anterior cruciate and posterolateral ligament injury.