Effects of a novel externally rotated trochlear design on patellofemoral kinematics in total knee arthroplasty: A cadaveric study

Purpose: To investigate whether a novel femoral component with a trochlear sulcus externally rotated (EXT) by 3°, mimicking the natural relationship between the posterior condylar axis (PCA) and epicondylar axis (EA), improves patellofemoral (PF) kinematics in total knee arthroplasty (TKA) by more closely replicating native patellar motion. Methods: A cadaveric study was conducted on 12 lower limbs from six fresh-frozen hemi-body specimens. After acquiring native knee kinematics using an optical navigation system, each knee underwent TKA with two prosthetic designs: a standard (STD) implant and an EXT variant with a 3° lateralized trochlear groove. Patellar kinematics were evaluated in flexion–extension movements, and quantified via root mean square error, correlation coefficient and normalized range relative to native conditions. Statistical comparisons were performed using the Wilcoxon signed-rank test. Results: Patellar flexion was similar across native and prosthetic conditions. However, the STD design showed significantly lower patellar misalignment than the EXT in terms of patellar shift (p < 0.01) and exhibited lower inter-specimen variability. The EXT design resulted in an inversion of patellar tilt patterns and demonstrated reduced correlation with native tilt kinematics. In terms of internal patellar rotation, patterns post-implantation were comparable between the STD and EXT designs, emerging beyond 50° of flexion. The expected benefits of trochlear external rotation were not confirmed. Conclusions: Although theoretically promising, the EXT trochlear design did not lead to improved replication of native PF kinematics. The findings suggest that trochlear sulcus lateralization alone is insufficient to restore physiological patellar tracking. Level of Evidence: Level V, cadaveric study.