ROBOTIC FUNCTIONAL ALIGNMENT NEUTRALIZES THE IMPACT OF EXTREME TIBIAL SLOPES (>8°): MINIMUM TWO-YEAR RESULTS OF A CONTINUOUS SERIES OF 269 MEDIAL UNICOMPARTMENTAL KNEE ARTHROPLASTIES

Introduction Tibial component positioning, and particularly tibial slope management, is a key determinant of success in unicompartmental knee arthroplasty (UKA). While robotic functional alignment allows implant positioning to be tailored to individual anatomy, the influence of extreme preoperative tibial slopes remains debated. The aim of this study was to evaluate whether a robotic planning strategy based on tibial slope optimization—through preservation or reasoned adjustment while maintaining ligament balance—could provide comparable clinical outcomes at a minimum 2-year follow-up regardless of native tibial slope. Materials and Methods This prospective study included 269 consecutive medial UKAs implanted using the Mako robotic system. The planning strategy aimed to optimize tibial slope by reducing excessive native slopes, increasing insufficient slopes, and preserving intermediate slopes. Patients were stratified according to preoperative radiographic tibial slope into three groups: high slope (>8°, n=89), standard slope (4–8°, n=126), and low slope (<4°, n=54). Outcome measures included accuracy of postoperative HKA alignment and tibial slope correction (robotic plan versus radiographic measurement), as well as IKS and KSS scores assessed at 2 months and 2 years. Results At 2-year follow-up, no significant differences in functional outcomes were observed according to preoperative slope category. The IKS score showed preoperative differences between groups (152.8 vs 142.4 vs 149.6; p=0.003), which disappeared by 2 months (p=0.35), with similarly excellent results at 2 years (193.3±15.7 vs 189.0±22.1 vs 193.8±13.2; p=0.25). KSS improved similarly across groups, with no significant difference at final follow-up (193.2 vs 188.7 vs 188.8; p=0.47). Mean HKA improved from 174.0° preoperatively to 176.7° postoperatively, with no intergroup difference. Tibial slope adjustment resulted in reduction in the high-slope group (10.0° to 5.1°, p<0.001), relative preservation in the standard group (6.2° to 4.8°), and slight increase in the low-slope group (3.1° to 3.9°, p=0.009). Robotic execution was precise, with a mean deviation of 0.7°. Final functional improvement was independent of native tibial slope (r=−0.019; p=0.80). Conclusion Robotic functional alignment appears to neutralize the impact of extreme native tibial slopes in medial UKA. By enabling precise, individualized tibial slope optimization, this strategy provides reproducible and excellent 2-year functional outcomes regardless of preoperative tibial morphology.