Biomechanical and anatomical effects of an external rotational torque applied to the knee: a cadaveric study.

Abstract

External rotational torque is one of the mechanisms that may occur during a pivoting or twisting injury to the knee. Simulated external rotational injury by applying external rotational torque will increase knee laxity and cause soft tissue damage to the knee. Controlled laboratory study. Six cadaveric knees and a custom testing system were used to produce external rotational torque of 30 degrees , 45 degrees , and 60 degrees with the knee at 30 degrees of flexion. Anterior-posterior, valgus-varus, and rotational knee laxity were quantified. After sequential rotational torque to 60 degrees , the specimens were dissected to identify injured structures. External rotational torque of 45 degrees and 60 degrees 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. External rotational torque to 60 degrees increased knee laxity, and dissection revealed a consistent pattern of injury to the medial and lateral collateral and anterior cruciate ligaments and posterolateral corner. Because isolated ligament injuries are rare, recognizing these combined ligamentous injuries early is essential for repair in the acute stage.