Small increases in patellar thickness significantly alter patellofemoral kinematics and joint loading

Anterior knee pain remains a leading cause of dissatisfaction following total knee arthroplasty (TKA), often without overt mechanical complications. The biomechanical consequences of altered patellar thickness remain incompletely understood. This study evaluated the effects of reconstructed patellar thickness on patellofemoral joint (PFJ) kinematics and kinetics using a cadaveric model.

Eleven knees from six unembalmed whole-lower-extremity cadaveric specimens were tested with a robotic simulator and optical motion capture. Patellar thickness was altered in three conditions: understuffed (-3 mm), neutral (native) and overstuffed (+4 mm). PFJ kinematics and contact forces were assessed during passive flexion and simulated stair descent. Total force and regional pressures at the medial facet C1, central ridge C2 and lateral facet C3 were recorded using a custom multi-sensor array.

Overstuffing significantly altered PFJ kinematics, including increased posterior translation (p < 0.001), reduced flexion (p = 0.001) and altered valgus alignment (p = 0.020). Composite PFJ force increased with thickness during passive flexion (overstuffed 59.9 N; neutral 33.9 N; understuffed 23.5 N; p < 0.001) and stair descent (50.5 N, 27.5 N, 17.9 N; p < 0.001). Regional analysis showed a lateral shift in loading, with the lateral facet most affected (p < 0.001). Understuffing reduced joint pressures with minimal kinematic change.

Small increases in reconstructed patellar thickness significantly alter PFJ motion and load distribution, particularly lateral facet forces. These results highlight the biomechanical sensitivity of the PFJ to thickness variation and support the need for thinner, modular or patient-specific components to enable finer intraoperative control. Restoring native geometry may help reduce anterior knee pain and dissatisfaction after TKA.

Level IV, controlled laboratory study.