Biomechanical evaluation of patellofemoral kinematics and interface forces under varying loading conditions in total knee arthroplasty with a novel femoral design for kinematic alignment

Patellofemoral complications remain a leading cause of dissatisfaction after total knee arthroplasty (TKA), with femoral component geometry, patellar resurfacing (PR), and quadriceps loading direction playing key roles in postoperative biomechanics. This PhD project investigated how different medial pivot femoral component designs influence the patellofemoral kinematics and the contact forces, and how these effects interact with PR and muscle loading conditions. Twelve paired cadaveric knees were tested in three conditions: native, TKA without PR, and TKA with PR. Six specimens received a traditional medial pivot femoral component and six a “patella-friendly” medial pivot design. Flexion–extension cycles were performed under controlled quadriceps loading, including induced variations in load direction. Patellofemoral kinematics were assessed using an optoelectronic motion capture system. To quantify contact forces after resurfacing, a novel instrumented patellar implant embedding two piezoresistive sensors was developed, enabling independent measurement of medial and lateral patellofemoral contact forces. Without resurfacing, the patella-friendly design more closely reproduced native patellofemoral kinematics. The traditional design showed greater patellar rotation in varus–valgus and tilt, whereas the patella-friendly design more closely matched native joint behavior. Moreover, the patella-friendly design was more tolerant to quadriceps loading variation. After resurfacing, inter-design kinematic differences were reduced, and both implants deviated significantly from native kinematics. However, the patella-friendly design promoted a more balanced medial–lateral distribution of patellofemoral contact forces. These findings provide new insights into the complex biomechanical interplay between femoral component geometry, patellar resurfacing, and quadriceps loading. The results may inform patient-specific preoperative planning, implant design refinement, and surgical alignment strategies. Furthermore, the developed instrumented patellar implant proved to be a promising in vitro tool for assessing contact mechanics and may support future intraoperative evaluation of implant positioning and bone resections.