Summary

The study aimed to quantify the effect of increased posterior tibial slope (PTS) on medial and lateral meniscus forces, finding that increased PTS led to a significant reduction in lateral meniscus forces at low flexion angles, with no significant changes in medial meniscus forces, suggesting a complex relationship between PTS and meniscal loading that warrants further investigation.

Abstract

Introduction

The menisci play a key role in knee stability, particularly in resisting anterior translation and rotation. Increased posterior tibial slope (PTS) has been identified as a significant risk factor for concomitant meniscal tear with ACL injury. To reduce the risk of meniscal injuries and ACL graft failure, surgeons may perform a PTS-reducing osteotomy during ACL revision. This study aimed to quantify the effect of increased PTS on the resultant forces in the medial and lateral meniscus.

Methods

A 6 degrees of freedom robotic testing system (MJT Model FRS2010) was used to apply external loads to 7 fresh-frozen human cadaveric knees (mean age, 50±13.4 years). The following loads were continuously applied from full extension to 90° flexion: (1) 5Nm internal tibial + 10Nm valgus torque, (2) 100N axial compression + 10Nm varus torque, and (3) 134N anterior load + 200N compression. Resultant forces in the meniscus were acquired for two PTS states: (1) Native PTS and (2) Increased PTS (Mean 7.4°±0.7°). To simulate the effects of PTS increase, an anterior opening wedge osteotomy was performed at the infra-tuberosity level. An external fixator was used to provide rigid fixation and allow for multiple PTS adjustments, changing the native PTS to increased PTS and back to native PTS. Thus, kinematics could be replayed from previously applied loading conditions before and after PTS change and the resultant forces in menisci in both PTS states were determined using the principle of superposition. The Mann-Whitney U test was used to compare the resultant forces in both the medial and lateral meniscus in 2 PTS states (native PTS, increased PTS) at 7 flexion angles (full extension, 15°, 30°, 45°, 60°, 75°, 90°). Significance was set at p < 0.05.

Results

No significant differences were found for medial meniscus forces across all loading conditions and flexion angles. In response to a 5Nm internal tibial and 10Nm valgus torque, the lateral meniscus force decreased by 45% at 15° flexion after increasing PTS (p < 0.05). A 10Nm varus torque and 100N compression reduced lateral meniscus force by 70% at 30° flexion (p < 0.05). No significant differences were observed at other flexion angles or loading conditions (p > 0.05).

Conclusion

The increase in PTS led to a reduction in the resultant forces in the lateral meniscus at low flexion angles. This outcome contradicts the initial hypothesis, which was informed by previous clinical studies examining the effect of PTS on intra-articular pathologies. Overall, the results indicated no significant changes in the resultant force in the medial meniscus or across most flexion angles in the lateral meniscus. These findings suggest that the influence of PTS on meniscal loading is more complex than previously recognized. Further research is necessary to investigate the differences between medial and lateral tibial PTS, as well as proximal tibial morphology, to better understand the biomechanical impact of PTS on meniscal forces.