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 ca daveric knees. The posterolateral ligaments sectioned included the lateral collateral and arcuate ligaments, the popliteofibular ligament, and the popliteal tendon at tachment to the tibia. Combined sectioning of the an terior cruciate and posterolateral ligaments resulted in maximal increases in primary anterior and posterior translations at 30° of knee flexion. Primary varus, pri mary internal, and coupled external rotation also in creased and were maximal at 30° of knee flexion. Com bined sectioning of the posterior cruciate and posterolateral ligaments resulted in increased primary posterior translation, primary varus and external rota tion, and coupled external rotation at all angles of knee flexion. Examination of the knee at 30° and 90° 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° 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.