Lateral prosthetic trochlear angle deviation is common and clinically safe after robotic functionally aligned total knee arthroplasty.

Purpose: The alignment between the prosthetic trochlear angle (PTA) and the quadriceps vector (QV) is thought to influence patellofemoral kinematics and clinical outcomes following total knee arthroplasty (TKA). The aim of this study was to evaluate whether the deviation of the PTA from the QV correlates with patient-reported outcomes in image-based, robotic-assisted, functionally aligned TKAs (FA-TKAs).

Methods: In this retrospective study, 237 patients undergoing image-based robotic-assisted FA-TKA between March 2021 and April 2023 were evaluated. Inclusion criteria required complete radiological and clinical data with at least 2 years of follow-up. The PTA-QV deviation was measured on post-operative long-leg radiographs. Clinical outcomes were assessed using the Knee Society Score (KSS), Knee Society Score-Functional (KSS-F) and Forgotten Joint Score (FJS).

Results: The mean PTA deviation from the QV was 3.8 ± 2.4°, predominantly laterally. Only 2.9% of knees exhibited medial deviation. At a mean follow-up of 34.3 ± 6.7 months, patients demonstrated excellent clinical outcomes. PTA deviation was correlated only with the final hip-knee-ankle (HKA) angle (p < 0.001) but showed no significant correlation with clinical scores.

Conclusion: In robotic-assisted, FA-TKAs, the PTA typically deviates laterally from the QV without correlating with patient outcomes. This mild lateral deviation primarily reflects overall coronal alignment and appears biomechanically safe, maintaining optimal post-operative knee function and patient satisfaction.

Level of evidence: Level IV.