The Role of Sagittal Tibial Tubercle-Trochlear Groove Distance in Patellofemoral Joint Loading: A Computational Modeling Analysis: Patellofemoral

Objectives: The tibial tubercle to trochlear groove (TT-TG) distance is a key metric for evaluating patellofemoral (PF) pathologies, with larger distances associated with instability and cartilage degeneration. The sagittal TT-TG (sTT-TG), measured as the horizontal distance from the trochlear groove to the tibial tubercle in the sagittal plane, has emerged as a potential indicator of increased PF pressures. Nonetheless, the connection between PF pressure and factors such as femoral rollback and patellar height remains unclear, but these elements are crucial for improving surgical techniques like tibial tubercle osteotomy (TTO). This study aimed to define the association between sTT-TG and PF contact pressure and examine how femoral rollback, patellar height, and joint line height affect sTT-TG and PF loading using a computational model. Methods: A two-dimensional sagittal knee model was developed, with the femur as a circle and patella as a rectangular block. Parameters including sTT-TG, patellar tendon angle (PTA), and PF contact pressure were calculated across 0°–140° flexion using femoral rollback data. Tibial tubercle position was varied (±10 mm), joint line height adjusted (±10 mm), and patellar tendon length altered (±30%) to simulate patella alta and baja. Sensitivity analysis quantified these effects. Results: Posteriorizing the tibial tubercle by 5 mm increased PF contact pressure by 10% at 0° and 0.8% at 30° flexion, while anteriorization by 10mm reduced it by 21.6% and 18.2% (R² > 0.985). The sTT-TG decreased 5.5 mm from 0° to 60° due to femoral rollback, then rose in deeper flexion. Patella baja increased contact pressure by 8.8%–9% at 0° and 30°, patella alta decreased it similarly, with sTT-TG changes minimal (<0.2 mm). Joint line shifts significantly affected contact pressure but not sTT-TG. Conclusion: This study demonstrates that the sagittal TT–TG is a biomechanically relevant measure for assessing PF contact pressure, particularly in early flexion. However, its diagnostic and surgical value must be interpreted with caution at varying degrees of flexion and considering that patellar height and joint line height significantly influence loading without proportionally affecting the sTT–TG value.