Robotic-Assisted unicompartmental knee arthroplasty restores native joint line height and reduces alignment outliers

PURPOSE: Registry data suggests that robotic-assisted unicompartmental knee arthroplasty (rUKA) significantly reduces all-cause revisions compared to conventional implantation (cUKA). This study aims to compare joint line-related parameters and their reconstruction accuracy between rUKA and cUKA. METHODS: Five databases were searched using a pre-defined strategy and inclusion criteria: (1) comparative studies reporting radiological outcomes, (2) human studies, (3) English language, and (4) meta-analyses for cross-referencing. Cadaveric or saw-bone studies were excluded. Data extracted included demographics data, pre- and postoperative radiological parameters (HKA, MPTA, LDFA, posterior tibial slope, femoral sagittal angle, joint line height, implant congruency), and outliers. A random-effects meta-analysis was conducted using mean difference (MD) and odds ratio (OR) as main effect estimators. Risk of bias was assessed using the Newcastle-Ottawa Scale (NOS), and publication bias was evaluated with funnel plots. RESULTS: A total of 18 studies assessing 2470 patients (1112 rUKA, 1358 cUKA) were included in the analysis. No significant baseline differences were found in age, sex, BMI, follow-up period, MPTA, LDFA, or tibial slope. Postoperative radiological parameters showed no significant differences between groups for HKA, LDFA, MPTA, or tibial slope (p > 0.05). Joint line height was significantly lower in cUKA compared to rUKA (MD = -1.37 mm, 95% CI: -2.06 to -0.69, p < 0.001). Outlier analysis revealed that rUKA had significantly fewer outliers across relevant radiological parameters, including HKA, joint line height, tibial slope, femoral flexion, femoral implant congruency, and medial, anterior, and posterior tibial congruency. CONCLUSION: Reporting pre- and postoperative mean alignment parameters undermines patient-specific anatomy reconstruction with advanced technologies. Outlier reporting showed significant variability, with limited evidence supporting its clinical relevance. Future studies should focus on patient-specific reconstruction and define clinical thresholds for outliers.