Does Lateral Extra-articular Tenodesis of the Knee Affect ACL Graft In situ Forces and Tibiofemoral Contact Pressures?

Abstract Purpose To quantify the effects of lateral extra-articular tenodesis (LET) on tibiofemoral compartment contact area and pressures, knee kinematics and forces. Methods Nine cadaveric knees were tested using a robotic testing system. Two loading conditions, 1) anterior tibial translational load coupled with axial compression and 2) internal tibial torque coupled with axial compression were applied for each knee state at full extension, 30o, 60o and 90o of knee flexion. Kinematic data was recorded for three knee states: ALC competent, ALC deficient , and post-LET using a 6-mm semitendinosus graft. In situ force in the ACL was quantified using the principle of superposition by comparing the change in force measured before and after the removal of the ALC. Contact area and pressures in each tibiofemoral compartment was measured by replaying kinematics after soft tissues were removed and pressure sensors inserted. Results In response to an anterior tibial translational load, mean contact area in the medial compartment decreased by 33.1% from the ALC competent to post-LET knee states at 90o of knee flexion (P = .042). No significant differences in the lateral compartment contact pressure were found between knee states. In situ force in the ACL in response to an anterior tibial translational load decreased by 43.4% and 50% from the ALC deficient to post-LET knee states at 60o (P = .02) and 90o (P = .006). No significant difference in kinematics was observed between the ALC competent and post-LET knee states in each of the loading conditions at all knee flexion angles (P > .05). Conclusions In this in vitro model, LET with a semitendinosus graft did not significantly overconstrain the knee nor increase pressure in the lateral compartment. Additionally, LET reduced the in situ force in the ACL in the setting of ALC injury.