Patellofemoral joint complications account for as much as half of all total knee arthroplasty revisions. Surgical alignment of the implants in the body may be varied within a narrow range and such variation has been shown to effect knee mechanics. The objective of this project was to better understand how prosthetic alignment affects patellofemoral joint mechanics and wear. Validated by experimental testing, a finite element model and computational wear simulation was developed and to evaluate the effect of component alignment on patellofemoral joint tracking, load transfer, and wear.

Patellofemoral joint load transfer and contact distribution were shown by experimental testing to be insensitive to external femoral rotation. Medialization of the patellar implant resulted in improved distal extensor kinematics, decreased PFJ contact loads, and more uniform PFJ contact distribution.

A computational wear simulation was successfully developed and implemented to study patellofemoral joint wear. The geometry and mechanics of the patellofemoral joint are more complicated than a conforming joint such as the hip. The continually changing contact conditions, complex sliding interaction, and plastic deformation present in the patellofemoral joint were all captured by the wear simulation. Patellar wear was studied over the course of a 10 year period for the case o f a neutral and 5° externally rotated femoral. Wear results suggested that the propensity of the patella to sublux laterally increased as patellar button wear progressed, and the patellar wear rate increased by 6% after 5° external femoral rotation. Wear was concentrated in the center, superior-lateral, and superior-medial zones of the patella, in agreement with clinical and experimental results reported in the literature.

Based on the findings of this study, placement of the patellar button to reproduce the native medial patellar ridge is recommended. In the knee system studied, external femoral rotation by 5° or less did not have a clinically significant effect on PFJ load transfer or kinematics. Alignment of the femoral component with the surgical epicondylar axis or up to 5° external, therefore, is left to the discretion of the surgeon.