The influence of internal and external tibial rotation offsets on knee joint and ligament biomechanics during simulated athletic tasks

Abstract

Background: Following anterior cruciate ligament injury and subsequent reconstruction transverse plane tibiofemoral rotation becomes underconstrained and overconstrained, respectively. Conflicting reports exist on how rotations influence loading at the knee. This investigation aimed to determine the mechanical effects of internal and external tibial rotation offsets on knee kinematics and ligament strains during in vitro simulations of in vivo recorded kinematics.

Method: A 6-degree-of-freedom robotic manipulator arm was used to articulate 11 cadaveric tibiofemoral joint specimens through simulations of four athletic tasks produced from in vivo recorded kinematics. These simulations were then repeated with 4° tibial rotation offsets applied to the baseline joint orientation.

Findings: Rotational offsets had a significant effect on peak posterior force for female motion simulations (P < 0.01), peak lateral force for most simulated tasks (P < 0.01), and peak anterior force, internal torque, and flexion torque for sidestep cutting tasks (P ≤ 0.01). Rotational offsets did not exhibit statistically significant effects on peak anterior cruciate ligament strain (P > 0.05) or medial collateral ligament strain (P > 0.05) for any task.

Interpretation: Transverse plane rotational offsets comparable to those observed in anterior cruciate ligament deficient and reconstructed patients alter knee kinetics without significantly altering anterior cruciate ligament strain. As knee degeneration is attributed to abnormal knee loading profiles, altered transverse plane kinematics may contribute to this. However, altered transverse plane rotations likely play a limited role in anterior cruciate ligament injury risk as physiologic offsets failed to significantly influence anterior cruciate ligament strain during athletic tasks.

Keywords: Anterior cruciate ligament; Athletic task simulation; Jump landing; Medial collateral ligament; Robotic manipulator.

Figure 1

Stages of the testing methodology presented. A) Resect soft tissue outside of the major knee ligaments, B) resect the patella and patellar tendon, C) mount prepared specimen to 6DOF load cell on the end effector of a robotic manipulator using custom fixtures, D) implant DVRT on distal aspect of the anteromedial bundle of the ACL, E) implant DVRT sensors on the midsubstance of the MCL, F) use the robotic manipulator to articulating the tibia about the stationary femur and simulate in vivo recorded kinematic pathways. Step F) is performed with the tibia in a neutral orientation as well as offset by a 4° internal rotation and offset by at 4° external rotation. Simulation is initiated with the specimen positioned to match the orientation of initial ground contact recorded for each task.

Figure 2

Depiction of peak ACL and MCL strain values and standard deviations for all three rotational offset conditions for each motion task simulated. For both ligaments, there were no statistically significant differences in peak strains between offset conditions.

Figure 3

Depiction of ACL and MCL strains values and standard deviations at initial contact for all three rotational offset conditions for each motion task simulated. For both ligaments, there were no statistically significant differences in initial contact strains between offset conditions.