Failure to Restore Normal Trochlear Orientation Does Not Affect Postoperative Patella-Related Outcomes in Robotic-Assisted Functional Alignment Total Knee Arthroplasty.

Background: This study evaluated the restoration of trochlear orientation following primary functional alignment (FA) total knee arthroplasty (TKA) using an image-based robotic-assisted system and investigated the relationship between trochlear orientation and clinical outcomes.

Methods: This retrospective study included 110 robotic-assisted TKAs performed between September 2021 and October 2023. The average age of this cohort was 67 ± 8.1 years, and the average follow-up duration was 24 ± 6.5 months. Radiographic and clinical analyses were conducted, including visual analog scale (VAS), range of motion (ROM), the Knee Society Score (KSS), and the Feller's patellar score (FPS). We measured the angles between the transepicondylar axis and posterior condylar axis (PCA), between the anterior trochlear line (ATL) and PCA, and between the lateral trochlear inclination and PCA, between the preoperative and postoperative Whiteside line, and sulcus angle (SA) to analyze the restoration of the trochlear orientation.

Results: The VAS, ROM, KSS, and FPS all showed significant improvement after FA-TKA (P < 0.001). Postoperatively, the proportion of abnormal SA was 88.7%, abnormal ATL was 56.4%, abnormal lateral trochlear inclination was 77.2%, and abnormal Whiteside line was 31.8%. Subgroup analysis showed that there was no significant correlation between the restoration of trochlear orientation and early- to mid-term knee function scores (VAS, ROM, KSS, and FPS; P > 0.05). Furthermore, multivariable logistic regression identified abnormal SA (odds ratio = 1.15; 95% confidence interval: 1.03 to 1.27; P = 0.009) and abnormal ATL (odds ratio = 1.57; 95% confidence interval: 1.26 to 1.97; P < 0.001) as independent risk factors for the severity of anterior knee pain at 30 days postoperatively.

Conclusions: In robotic-assisted FA-TKA, most cases failed to restore natural trochlear orientation and shape. This discrepancy did not significantly affect patellar scores or knee function at 30-day and 2-year follow-up. But abnormal SA and ATL may be related to anterior knee pain at 30 days postoperatively.