Impact of Alignment Strategies on Trochlear Morphology Following Robotic-Assisted Total Knee Arthroplasty

Dr. Abinash Ghadei, Dr. Aurobinda Das

Abstract: Purpose: Restoration of native trochlear morphology remains a challenge in total knee arthroplasty (TKA), especially given the variability in coronal alignment strategies, including mechanical alignment (MA), adjusted mechanical alignment (aMA), kinematic alignment (KA), and functional alignment (FA). Emerging evidence suggests that kinematic-based techniques may better replicate native trochlear orientation compared to mechanical approaches [1, 2]. This study aimed to evaluate the impact of these four alignment techniques on postoperative trochlear orientation in patients undergoing robotic-assisted TKA (RAS-TKA). We hypothesised that FA would demonstrate the fewest deviations from native trochlear parameters. Methods: A prospective analysis was conducted on 96 patients undergoing RAS-TKA using a single prosthetic design. Preoperative planning incorporated both mechanical and kinematic alignment considerations. Intraoperative alignment was achieved through aMA in 68 patients and FA in 28 patients following robotic balancing protocols. Preoperative transverse CT imaging was employed to assess native anatomical parameters, including posterior condylar axis (PCA), lateral trochlear inclination (LTI), sulcus angle (SA), and anterior trochlear line (ATL) angle. Postoperative measurements were derived from intraoperative robotic software and photographic implant analysis. Deviation from native orientation was quantified, with outliers defined as ?3? deviation. Trochlear dysplasia was classified by LTI <12?1. Results: The median native values were: PCA 2?, LTI 18?, SA 137?, and ATL 4?. Outlier prevalence for LTI ranged from 47% to 60% across alignment types, with KA producing the fewest outliers, followed by FA, aMA, and MA. Similar trends were observed for ATL deviation (outlier range: 40.5%?85%). SA exhibited the highest alteration, with 81% of cases classified as outliers. Only LTI under KA alignment did not significantly differ from the native anatomy (p > 0.05). Conclusion: Significant deviation from native trochlear orientation occurs after RAS-TKA irrespective of alignment strategy. Kinematic alignment yielded the most accurate replication of lateral trochlear inclination, although a substantial rate of outliers remained. The standardised design of contemporary implants may necessitate trade-offs between flexion balance and anatomical restoration of the trochlea. Further longitudinal studies are warranted to determine the clinical impact of these anatomical compromises on patellofemoral function and patient outcomes.

Keywords: alignment, patellofemoral joint, robotic?assisted, total knee arthroplasty, trochlea orientation