Patellofemoral alignment safe zones in robotic-assisted TKA do not affect outcomes but do influence patellar resurfacing rates.

Purpose: Anterior compartment management remains a challenging aspect of total knee arthroplasty (TKA), particularly in personalised alignment strategies. This study aimed to assess whether restoring patellofemoral alignment parameters within predefined safe zones-specifically patellar tilt (PTi), patellar translation (PTr) and patellar offset (PO)-is associated with improved clinical outcomes following robotic-assisted TKA (rTKA).

Methods: This retrospective study included 283 patients who underwent primary rTKA between March 2021 and January 2023 using functional alignment (FA) or functional knee positioning (FKP) principles. All surgeries were performed using a CT-based robotic system (Mako, Stryker). Patients were stratified into groups based on radiographic values of PTi, PTr and ΔPO, using thresholds derived from prior robotic studies to define safe zones. Clinical outcomes at a mean follow-up of 2.8 ± 0.8 years included Knee Society Score (KSS), Forgotten Joint Score-12 (FJS-12) and Kujala Anterior Knee Pain Scale (AKPS).

Results: There were no statistically significant differences in final KSS, FJS-12 or AKPS between groups within or outside the safe zones for PTi, PTr or ΔPO. However, patients with PTi < 0°, ΔPO > 0 mm (overstuffing) or PTr within ±2 mm showed significantly higher rates of patellar resurfacing (p < 0.001). No group demonstrated superior clinical outcomes across the three parameters studied.

Conclusion: Restoring patellofemoral alignment parameters within predefined safe zones was not associated with improved short-term clinical outcomes in rTKA. Robotic-assisted FA provides accurate restoration of the anterior compartment, reducing reliance on patellar resurfacing in eligible patients. Our data suggest that target biomechanical parameters can potentially be achieved without resurfacing in cases where it is not indicated. Our hypothesis that patients within the proposed safe zones would demonstrate improved clinical outcomes was not supported by the current results. Further prospective studies are needed to determine whether femoral safe zones can predict long-term benefit.

Level Of Evidence: Level II.