Summary
In knees with high tibial slope, slope reducing HTO and LET offload the ACL differently; therefore, specific ACL loading mechanisms should be considered when selecting these adjunctive surgeries to ACL reconstruction.
Abstract
Introduction
In ACL-injured individuals with increased tibial slope, adjunct treatments to ACL reconstruction (ACLR) may help reduce the risk of graft failure. These treatments include slope-reducing high tibial osteotomy (SR-HTO) and lateral extra-articular tenodesis (LET). While both interventions can decrease graft failure risk, their biomechanical effects, particularly in knees with increased tibial slope, remain unclear. This study compared the effects of SR-HTO and LET on ACL force and tibiofemoral kinematics in knees with high tibial slope using computational modeling.
Methods
Computational models of the tibiofemoral joint were developed from ten cadaveric right knees (five male, five female; age: 33±7 years). MRI and CT scans were used to reconstruct 3D geometries of the bones, cartilage, and menisci. The tibial geometries were then imported into reverse engineering software, where a virtual anterior opening wedge osteotomy increased the tibial slope to 15°, and a closing wedge SR-HTO reduced it to 5°. The geometries of the tibia, and the femur, cartilage, and meniscal geometries along with meniscal and ligament attachment data, were then imported into ADAMS multi-body dynamic software, incorporating standardized ligament properties (slack lengths and stiffnesses). For knees with a 15° tibial slope, lateral extra-articular tenodesis (LET) was simulated by tensioning lateral tissues to 21 N at 60° of flexion. Three conditions were simulated for each knee: 1) high tibial slope of 15°, 2) SR-HTO, and 3) LET. Three loading scenarios were applied to each condition: 1) 100 N axial compression, 2) axial compression with an 8 Nm valgus moment, and 3) axial compression, valgus moment, 4 Nm internal rotation moment, and 30 N anterior force to simulate a pivot shift exam. All loads were applied with the knee at 15° of flexion, with the femur fixed, and the tibia free to move except in flexion. Outcome measures included ACL force at peak applied loads and tibiofemoral kinematics, specifically anterior tibial translation (ATT) and internal tibial rotation (ITR). Results were compared using a nonparametric Friedman test with Least Significant Difference post-hoc correction (alpha=0.05).
Results
Under axial compression, only SR-HTO reduced median ACL force by 69% compared to the high-slope knee (p<0.01). Under compression and valgus, SR-HTO and LET reduced ACL force by 32% (p<0.01) and 43% (p<0.01), respectively. Under a simulated pivot shift, LET reduced ACL force by 58% (p<0.001) compared to the high-slope knee and 34% (p<0.05) compared to SR-HTO. Regarding kinematics, under compression, SR-HTO decreased median ATT by 34% (p<0.05). Under compression and valgus, SR-HTO and LET reduced ITR by 25% (p<0.01) and 16% (p<0.05), respectively. Under a simulated pivot shift, LET reduced ITR by 22% (p<0.01).
Discussion
In knees with increased tibial slope, SR-HTO and LET offload the ACL by affecting kinematics differently depending on the loading scenario. With compression, SR-HTO reduced ATT, but LET did not. With compression and valgus, both SR-HTO and LET reduced coupled ITR. During a simulated pivot shift, only LET reduced ITR, because the lateral tissue acts as a checkrein against internal rotation torque.