Quantification of the role of tibial posterior slope in knee joint mechanics and ACL force in simulated gait

The anterior cruciate ligament (ACL) rupture is a common knee joint injury with higher prevalence in female athletes. In search of contributing mechanisms, clinical imaging studies of ACL-injured individuals versus controls have found greater medial-lateral posterior tibial slope (PTS) in injured population irrespective of the sex and in females compared to males, with stronger evidence on the lateral plateau slope. To quantify these effects, we use a lower extremity musculoskeletal model including a detailed finite element (FE) model of the knee joint to compute the role of changes in medial and/or lateral PTS by ±5° and ±10° on knee joint biomechanics, in general, and ACL force, in particular, throughout the stance phase of gait. The model is driven by reported kinematics/kinetics of gait in asymptomatic subjects. Our predictions showed, at all stance periods, a substantial increase in the anterior tibial translation (ATT) and ACL force as PTS increased with reverse trends as PTS decreased. At mid-stance, for example, ACL force increased from 181 N to 317 N and 460 N as PTS increased by 5° and 10°, respectively, while dropped to 102 N and 0 N as PTS changed by -5° and -10°, respectively. These effects are caused primarily by change in PTS at the tibial plateau that carries a larger portion of joint contact force. Steeper PTS is a major risk factor, especially under activities with large compression, in markedly increasing ACL force and its vulnerability to injury. Rehabilitation and ACL injury prevention programs could benefit from these findings.