Posterior tibial slope is linearly related to anteroposterior shift of the tibiofemoral contact mechanics: A biomechanical study.

Abstract

To investigate the changes in tibiofemoral contact mechanics following an infra-tubercle slope-modifying osteotomy. An infra-tubercle slope-modifying osteotomy was performed on eight fresh-frozen cadaveric knees and fixed with an external fixator, which allowed for accurate slope adjustments from 15° to 0° in 5° increments. The specimens were axially loaded at 400 N using a custom-made, free-pivoting rig. Using a high-resolution pressure sensor, the anteroposterior and mediolateral centre of force (COF) migration and the tibiofemoral pressure characteristics, including contact area, mean pressure and peak pressure, were recorded for different tibial slope adjustments at 0°, 30°, 60° and 90° of knee flexion. These were repeated after cutting the anterior cruciate ligament (ACL). A two-way repeated measures analysis of variance was used to compare the different test conditions. Pearson's correlation and linear regression were used to analyse the relationship between tibial slope and COF migration. Statistical significance was set at p < 0.05. Regardless of flexion angle and ACL integrity, the tibial slope showed a strong and linear association with anteroposterior COF shift (all Pearson's r < -0.93; p < 0.01). Decreases in posterior tibial slope resulted in significant anterior translation of the COF at any flexion angle (p < 0.05). ACL deficiency further increased the anterior COF shift compared to the ACL-intact state (p < 0.05) after decreasing tibial slope. There were no significant mediolateral COF shifts or changes in contact area, mean pressure or peak pressure in the lateral and medial tibiofemoral compartments, regardless of the extent of the slope adjustment. Changing tibial slope alters the knee joint contact mechanics, with tibial slope demonstrating a strong linear correlation with anteroposterior tibiofemoral contact migration. Decreasing tibial slope redistributes the contact mechanics anteriorly, thereby unloading the posteromedial and posterolateral compartments. This further increases in cases of ACL instability and a steep posterior tibial slope. Therefore, a slope-reducing osteotomy may effectively unload frequently prematurely degenerated posterior tibiofemoral compartments in cases of recurrent ACL instability. N/A.