The Trochlear Paradox in Native Knees and Its Potential Impact on Total Knee Arthroplasty: An MRI-Based Correlation Study Investigating the Effect of Varying Posterior Femoral Condyle Angles on the Patellofemoral Joint

Abstract

Background: Since the beginning of total knee arthroplasty, implant alignment has been a central point of discussion. As diverse as the discussed alignment theories are, as uniform is the implant design, which is supposed to be based on the “average knee.” Steady upgrades in prosthesis design and modern alignment theories have achieved improvements. However, knee arthroplasty continues to be burdened by a significant percentage of dissatisfied patients. In current knee arthroplasty, femoral implant alignment is referenced by the dorsal and distal condylar axes. The patellofemoral joint variance is not sufficiently considered. Predominantly dorsal and distal referencing at the femoral condyle determines the postoperative shape of the anterior knee joint. The present study investigated a possible relationship between dorsal and distal joint parameters and the patellofemoral joint. Methods: In this explorative retrospective monocentric study, MRI cross-sectional images of 100 native knee joints were evaluated. By determining parametric correlations according to Pearson, the study investigates whether the independent variables “posterior femoral condyle angle” and “lateral distal femoral angle” are related to “lateral trochlear inclination”, “patella tilt”, and “bisect offset”. Results: The posterior condylar angle significantly correlates with lateral trochlear inclination, patella tilt, and bisect offset. There is a positive correlation with patella tilt and bisect offset but a negative correlation with lateral trochlear inclination. The lateral distal femoral angle did not correlate with the studied parameters. Conclusion: The lateral trochlear inclination decreases with an increased posterior femoral condylar angle. The posterior referencing of the femoral component in total knee arthroplasty simultaneously establishes the shape of the anterior knee joint. Our results indicate that increasing posterior condyle angles significantly correlate with flattened lateral trochlear inclinations in native knees and suggest a systematic biomechanical conflict in total knee arthroplasty.