Biomechanical and Anatomical Effects of an External Rotational Torque Applied to the Knee

Abstract

Background External rotational torque is one of the mechanisms that may occur during a pivoting or twisting injury to the knee. Hypothesis Simulated external rotational injury by applying external rotational torque will increase knee laxity and cause soft tissue damage to the knee. Study Design Controlled laboratory study. Methods Six cadaveric knees and a custom testing system were used to produce external rotational torque of 30°, 45°, and 60° with the knee at 30° of flexion. Anterior-posterior, valgus-varus, and rotational knee laxity were quantified. After sequential rotational torque to 60°, the specimens were dissected to identify injured structures. Results External rotational torque of 45° and 60° significantly increased knee joint laxity in all directions (P <. 05). Dissection showed that all posterior cruciate ligaments were intact; all medial collateral and anterior cruciate ligaments revealed either partial or complete tears. The lateral collateral ligaments were torn in all specimens. The popliteus tendon was attenuated in 1 specimen and was completely torn in 1 specimen. The popliteofibular ligament was torn in 3 specimens. Conclusion External rotational torque to 60° increased knee laxity, and dissection revealed a consistent pattern of injury to the medial and lateral collateral and anterior cruciate ligaments and posterolateral corner. Clinical Relevance Because isolated ligament injuries are rare, recognizing these combined ligamentous injuries early is essential for repair in the acute stage.