Patellar thickness can critically impact knee joint biomechanics after total knee arthroplasty

Despite the potential benefits of an increased moment arm of the knee extensor mechanism with a thicker patellar button in patients undergoing total knee arthroplasty (TKA), many surgeons are reluctant to alter the natural patellar thickness (PTh) during resurfacing. Clinically, this hesitation stems from concerns about straining the extensor apparatus under passive motion exercises and the potential consequences on postoperative joint biomechanics, but also because many patients with a thinner patella experience improved functionality, range of motion, and possibly also reduced soft-tissue pain in the short term postoperatively. However, the biomechanical relationships underlying such short- and long-term consequences remain unexplored. Our aim was to investigate the influence of PTh on knee biomechanics after TKA.

This study used advanced computational modelling techniques to undertake a systematic exploration of the influence of PTh variation on knee joint kinematics, contact mechanics, and muscle and soft-tissue loading patterns during level walking and squatting.

Our results indicate that increased PTh efficiency enhances the extensor mechanism, which is consistent with previous studies, but our investigation additionally demonstrates the reduction in tibiofemoral loading conditions, especially at higher flexion angles. Conversely, a thinner patella induces reduced patellofemoral contact forces and pressure, and may offer increased joint range of motion.

PTh was found to influence knee biomechanics in clinically relevant ways. A modest increase in thickness improved quadriceps efficiency and reduced tibiofemoral forces by up to ~10%, but also raised patellofemoral pressures by up to ~5 MPa. Conversely, thinner buttons lowered patellofemoral loading and may facilitate early comfort and flexion. These trade-offs were consistent across implant congruency designs, highlighting the need for patient-specific resurfacing strategies.