Sagittal Slope-Reducing High Tibial Osteotomy Decreases Anterior Cruciate Ligament Force and Coupled Internal Tibial Rotation Under Pivoting Loads: A Computational Modeling Study

Background: Sagittal-plane slope-reducing high tibial osteotomy (HTO) can reduce the risk of anterior cruciate ligament (ACL) injury in knees with a high posterior tibial slope. The biomechanical effect of slope-reducing HTO on tibiofemoral kinematics and force carried by the ACL remains less well understood. Hypothesis: Decreased tibial slope will be associated with decreased ACL force, coupled internal tibial rotation (ITR), and anterior tibial translation (ATT) under both compressive and combined compressive and valgus loads. Study Design: Descriptive laboratory study. Methods: Computational models of 10 cadaveric knees were created using magnetic resonance imaging– and computed tomography–based 3-dimensional renderings of the bones, articular cartilage, and menisci. Virtual slope-reducing HTO was performed on each tibial geometry in 1° increments, creating tibial slopes spanning −5° to 15°. All knees were flexed to 15°, and loads consisting of (1) axial compression (100 N) and (2) combined axial compression (100 N) and valgus torque (8 N·m) were then applied to each knee at each tibial slope. The outcome measures were ACL force, coupled ITR, and ATT. Relationships between tibial slope and each outcome measure were assessed via linear regression (α = .05), and the effects of 10° slope-reducing HTO, from 15° to 5°, on each outcome measure were reported. Results: A 10° slope-reducing HTO decreased ACL force by 53% under compression (1.7 N of ACL force per degree decrease in tibial slope; P < .001) and 47% under combined compression and valgus (4.7 N of ACL force per degree decrease in tibial slope; P < .001). Regarding kinematics, a 10° slope-reducing HTO decreased coupled ITR by 64% under combined compression and valgus (0.99° of coupled ITR per degree decrease in tibial slope; P < .001). Finally, a 10° slope-reducing HTO decreased ATT by 54% under compression (0.14 mm of ATT per degree decrease in tibial slope; P < .001). Conclusion: Slope-reducing HTO decreased ACL force linearly by reducing ATT with compression and also by decreasing coupled ITR with combined compression and valgus. Clinical Relevance: Slope-reducing HTO decreased ATT and coupled ITR, dampening movements known to load the ACL. These findings may provide a further biomechanical basis for the ability of slope-reducing HTO to decrease the risk of ACL injury.