The effects of ACL deficiency on mediolateral translation and varus-valgus rotation

Background: The anterior cruciate ligament (ACL) constrains the anterior translation and axial rotation of the tibia. However, the effect of ACL injury on the mediolateral translation and varus-valgus rotation of the tibia is unknown. Because of the oblique orientation of the ACL, we hypothesized that ACL deficiency alters mediolateral translation and varus-valgus rotation. Methods: The kinematics of 9 cadavers from full extension to 90° of flexion under various loading conditions were measured before and after ACL resection using a robotic testing system. Results: ACL deficiency increased the medial translation of the tibia and valgus rotation, especially at 15° and 30° of flexion. For example, at 15°, ACL deficiency increased the medial translation from 1.2 (SD 0.9) mm to 1.8 (SD 1.1) mm in response to a quadriceps load. The valgus rotation also increased from 0.8° (SD 0.6) to 1.7° (SD 0.8). Interpretation: ACL deficiency altered both the mediolateral tibial translation and valgus-varus rotation under various loading conditions. The increased medial tibial translation could shift the contact in the medial compartment towards the medial tibial spine, a region where degeneration is observed in ACL-deficient patients. In addition to restoring anterior laxity, ACL reconstruction might need to restore the mediolateral translation of the tibia and varus-valgus rotation of the knee. Copyright