Increasing the posterior tibial slope lowers in situ forces in the native ACL primarily at deep flexion angles

Abstract

High tibial osteotomy is becoming increasingly popular but can be associated with unintentional posterior tibial slope (PTS) increase and subsequent anterior cruciate ligament (ACL) degeneration. This study quantified the effect of increasing PTS on knee kinematics and in situ forces in the native ACL. A robotic testing system was used to apply external loads from full extension to 90°flexion to seven human cadaveric knees:(1) 200 N axial compressive load, (2) 5 Nm internal tibial + 10 Nm valgus torque, and (3) 5 Nm external tibial + 10 Nm varus torque. Kinematics and in situ forces in the ACL were acquired for the native and increased PTS state. Increasing PTS resulted in increased anterior tibial translation at 30°(1.8 mm), 60°(1.7 mm), and 90°(0.9 mm) flexion and reduced in situ force in the ACL at 30°(57.6%), 60°(69.8%), and 90°(75.0%) flexion in response to 200 N axial compressive load. In response to 5 Nm internal tibial + 10 Nm valgus torque, there was significantly less (39.