Meniscal forces and knee kinematics are affected by tibial slope modifying high tibial osteotomy

Purpose: To quantify the effect of increasing the posterior tibial slope (PTS) on knee kinematics and the resultant medial and lateral meniscal forces. Methods: In this controlled laboratory study, a 6 degrees of freedom (DOF) robotic testing system was used to apply external loading conditions to seven fresh-frozen human cadaveric knees: (1) 200-N axial compressive load, (2) 5-N m internal tibial +10-N m valgus torque and (3) 5-N m external tibial + 10-N m varus torque. Knee kinematics and the resultant medial and lateral meniscal forces were acquired for two PTS states: (1) native PTS and (2) increased PTS. Resultant forces in the medial and lateral meniscus were calculated using the principle of superposition. Results: In response to 5-N m external tibial + 10-N m varus torque, significantly more internal tibial rotation was observed after increasing PTS at 60° (p = 0.0156) and 90° (p = 0.0156) flexion. Increasing PTS caused significantly more medial tibial translation from 30° to 90° flexion in response to 5-N m internal tibial + 10-N m valgus torque. In response to 5-N m external tibial + 10-N m varus torque, the resultant force in the medial meniscus at 60° flexion decreased significantly after increasing PTS (32.8%, p = 0.016). Resultant forces in the lateral meniscus decreased significantly after increasing PTS at 30° (34.5%; p = 0.016) and 90° (29.7%; p = 0.031) flexion in response to 5-N m internal tibial + 10-N m valgus torque. Conclusion: Increasing PTS in a native knee with intact cruciate ligaments affected 6 DOF knee kinematics and decreased resultant forces in the medial and lateral meniscus by up to 35% in response to combined rotatory loads. Therefore, increasing PTS during high tibial osteotomy in a knee with intact cruciate ligaments does not increase the force carried by the entire meniscus at time zero. Level of Evidence: N/A.