Different intraoperative joint laxity patterns do not impact clinical outcomes in robotic-assisted medial unicompartmental knee replacement with 1-to-1 surface reconstruction

Purpose: Robotic-assisted technology in medial unicompartmental knee arthroplasty (mUKA) allows for customized adjustments of joint laxity through virtual preoperative component positioning before bone preparation. Nevertheless, the optimal balancing curve has yet to be delineated. This study sought to investigate if varying intraoperative knee laxity patterns had any impact on postoperative patient outcomes. Materials and Methods: A retrospective analysis was conducted on prospectively collected data from 326 fixed-bearing RAUKA procedures performed between 2018 and 2022 with a minimum 2-year follow-up. Patients were categorized into three cohorts based on intraoperative joint laxity patterns (millimetres of joint gap during valgus stress) imparted at 20 degrees, 60 degrees, 90 degrees and 120 degrees of knee flexion: cohort 1 < +0.5 mm (tight); cohort 2 between 0.6 and 1.9 mm (physiologic); cohort 3 > 2 mm (loose). Wilcoxon and Kruskal-Wallis tests were conducted to assess patient-reported outcome measure (PROM) improvements and preoperative and postoperative differences across the cohorts. A Spearman's test evaluated the correlation between knee balance at all degrees of flexion and preoperative and postoperative HKA. Results: No differences in preoperative and postoperative PROMs were identified across the cohorts (p > 0.05). All three cohorts with different joint laxity patterns showed a significant improvement in the postoperative PROMS (p < 0.05). The preoperative or postoperative limb alignment did not significantly affect clinical outcomes relative to different laxity patterns. Conclusion: No differences were found in the outcomes across different joint laxity patterns in robotic-assisted medial UKA using fixed-bearing mUKAs. There was no evident advantage for maintaining a closer to physiologic laxity compared to tighter or looser balancing.