Finite Element Investigation of Patellofemoral Contact Mechanics: Influence of Tibial Tuberosity Lateralisation and Trochlear Dysplasia on Extensor Mechanism Stability.

backgroundPatellofemoral instability arises from the interplay between trochlear morphology and malalignment of the extensor vector. Although each factor is individually well described, their combined mechanical effects have not been quantified within a single finite element framework.

objectiveTo investigate how lateral trochlear inclination (LTI) and tibial tuberosity position interact to influence patellofemoral contact mechanics and stability across clinically relevant knee flexion angles.

methodsA subject-specific finite element model of the femur-patella-tibia complex was reconstructed from high-resolution CT data. Cortical and cancellous bone, patellar cartilage, the MPFL, and patellar tendon were included. Three trochlear morphologies were simulated (LTI = 15°, 10°, 5°) under native alignment (Case A) and after 10 mm lateral tibial tuberosity translation (Case B). Flexion at 30°, 60°, and 90° was imposed via solver-applied tibial displacement. Primary outcomes were contact pressure, contact area, MPFL stress, and lateral patellar translation. Instability was defined as >5 mm lateral translation or >50% reduction in contact area, consistent with the biomechanical literature. Model convergence (<5% variation) and validation against cadaveric pressure data were performed; a sensitivity analysis tested material property variation (±15%).

resultsThe native model reproduced peak pressures (3.6 MPa at 60°) within 9% of experimental benchmarks. Decreasing LTI enlarged the contact patch and lowered mean pressures (-18%) but increased MPFL stress (+37%). Tibial tuberosity lateralisation reduced mean pressures further (-25%), yet, when combined with shallow trochlear slopes (≤8°), produced >5 mm lateral patellar translation and near-complete loss of cartilage contact by 60°, simulating lateral dislocation. Sensitivity testing confirmed robustness to material property uncertainty.

conclusionsShallow trochlear inclination dissipates articular load but destabilises the patella, an effect magnified by tibial tuberosity lateralisation. While these findings highlight thresholds at which stability may be compromised, they derive from a single-subject model and should be interpreted as hypothesis-generating rather than prescriptive. Broader validation across multiple geometries and loading conditions is required before clinical translation.