Impact of Femoral and Tibial Torsion on Patellofemoral Loading in Individuals With Patellofemoral Instability.

Patellofemoral stability is affected by several morphological factors including torsional alignment. To elucidate the impact of factors responsible for the stability of the patellofemoral joint, biomechanical research utilizes the analysis of joint contact forces. At present, there is a paucity of modeling-based research examining the influence of lower limb torsion on patellofemoral joint loading in individuals with patellofemoral instability. The objective of this study was to investigate the impact of the femoral version and tibial torsion on the patellofemoral joint loading. Musculoskeletal simulations were conducted based on 3D motion capture data of 40 individuals with patellofemoral instability using OpenSim. We created three models with different lower limb torsions for each participant: (i) generic torsion, (ii) personalized lower limb (femur and tibia) torsion, and (iii) isolated personalized femoral version model. We correlated femoral version and tibial torsion to differences in patellofemoral joint loading, muscle forces, and lever arms between models. Tibial torsion correlated to differences in mediolateral patellofemoral force (ρ = 0.39), whereas the femoral version showed no significant correlation to the differences in mediolateral patellofemoral force (ρ = 0.01). Notably, when neglecting individual tibial torsion, the femoral version correlated to differences in mediolateral patellofemoral force (ρ = 0.65). The femoral version can increase the lateralizing force on the patella, but this effect diminishes when addressing whole lower limb torsion in musculoskeletal simulations. Studies investigating solely the femoral version should, therefore, be interpreted with caution. Our findings underscore the necessity of evaluating whole lower limb torsion for a comprehensive assessment of its impact on patellofemoral stability and planning treatments. Level of Evidence: Retrospective cohort study, Level III.