Biomechanical consequences of patellar component medialization in total knee arthroplasty

The optimal amount of patellar component medialization in knee arthroplasty is unknown. We measured the impact, on patellofemoral kinematics and contact force distribution, of 0.0-, 2.5-, and 5.0-mm patellar component medialization in 7 cadaveric specimens implanted with knee arthroplasty components. The knees were flexed dynamically in a weight-bearing rig. Medialization led to lateral shift of the patellar bone, slight medial shift of the patellar component in the femoral groove, lateral tilt of the patella, reduced patellofemoral contact force in later flexion, and lateral shift of the center of pressure in early flexion. Effects on shift and tilt were proportional to the amount of medialization. As a result of this investigation, we recommend medializing the patellar component slightly-on the order of 2.5 mm.