Summary

A slope reducing HTO and LET have differential mechanisms of dampening ACL force where an HTO mitigates anterior tibial translation under compression while an LET decreases internal tibial rotation under pivoting loads.

Abstract

Introduction

Adjunct treatments to ACL reconstruction (ACLR), such as slope reducing high tibial osteotomy (HTO) or lateral extraarticular tenodesis (LET), can decrease risk of ACL graft failure. It is unclear how these interventions compare biomechanically in knees with high tibial slope. Thus, we employed a previously published computational knee model to address the following question. In knees with high tibial slope, what are the relative effects of a sagittal slope reducing HTO versus an LET on ACL force and tibiofemoral kinematics?

Methods

Computational models of eight, high-sloped cadaveric knees (four male, four female; age: 33.0±6.9 years) were developed using 3D geometries of the bones, cartilage, and menisci obtained from CT and MRI. These geometries along with ligamentous structures, were imported into multi-body dynamics software. The high-sloped knees had a lateral tibial plateau slope of 15°. Two surgical interventions were simulated in each high-sloped knee: 1) 10° slope reducing HTO and 2) Lemaire LET. Finally, three sets of loads were applied to each high sloped knee and to each knee after both slope reducing HTO and LET. The applied loads were 1) 100N compression; 2) 100N compression, 8Nm of valgus torque; and 3) a simulated pivot shift consisting of 100N compression, 8Nm valgus, 4Nm internal rotation torque and 30N anterior force. Outcome measures were ACL force at the peak applied loads and tibiofemoral kinematics including anterior tibial translation (ATT) and internal tibial rotation (ITR). Each outcome between the surgical conditions was compared for three loading scenarios using a nonparametric Friedman test with Least Significant Difference post-hoc correction (α=0.05).

Results

Under isolated compression, 10° slope reducing HTO decreased ACL force by 69% when compared to the high-sloped knee (p<0.01, Fig. 2). Under compression and valgus, slope reducing HTO and LET both reduced ACL force by 32% (p<0.01) and 43% (p<0.01), respectively. Under a simulated pivot shift, slope reducing HTO and LET reduced ACL force by 34% (p≤0.05) and 58% (p<0.001), respectively. Regarding kinematics, under compression, median ATT decreased by 34% with slope-reducing HTO (p<0.05). Under compression and valgus, both HTO and LET decreased ITR by 25% (p<0.01) and 16% (p<0.05), respectively. Finally, under a simulated pivot shift LET reduced ITR by 22% (p<0.01).

Discussion

Slope-reducing HTO and LET have differential ability to offload the ACL based on the applied loads. With a simulated pivot shift, the LET dampened ACL force more than the 10° slope reducing HTO. This likely stems from the LET checkrein to resist applied internal rotation moments. In contrast, under compression, slope-reducing HTO more strongly offloaded the ACL by reducing coupled ATT. Both surgical interventions offloaded the ACL under valgus load by reducing coupled ITR. Thus, slope-reducing HTO may have a more effective role in the anteriorly subluxating knee whereas an LET may be more protective in the rotationally unstable knee. Accordingly, the differential mechanisms of action of these two adjunctive procedures suggest there may be a role for both in the setting of a high sloped knee.