Discordant Results by Study Design: A Systematic Review and Meta-Analyses of Mobile versus Fixed Bearing for Unicompartmental Knee Arthroplasty.

Abstract

Previous reviews comparing mobile-bearing and fixed-bearing implants in unicompartmental knee arthroplasty report mixed results. It has yet to be explored whether such differences are influenced by study design. This systematic review and meta-analysis aimed to compare adverse events, patient-reported outcomes, and range of motion between the two implant types, overall and by study design (randomized trial, observational study, and registry study). We searched three databases up to February 4, 2025, for primary research studies comparing mobile- and fixed-bearing implants in unicompartmental knee arthroplasty patients. The outcomes of interest were adverse events, patient-reported outcomes, and range of motion. We performed Dersimonian-Laird random-effects meta-analyses, stratified by study design; assessed the risk of bias using the Cochrane and Risk Of Bias In Non-Randomized Studies - of Interventions tools; and assessed the certainty of the evidence using the Grading of Recommendations Assessment, Development, and Evaluation framework. A total of 30 observational studies (9,454 patients), six randomized trials (485 patients), and three registry studies (60,461 patients) were included. The meta-analyses found that fixed-bearing implants lowered the risk of revision (relative risk (RR) 0.65 [95% confidence interval (CI) 0.48 to 0.86]) and dislocation (RR 0.16 [95% CI 0.07 to 0.37]) and improved Western Ontario and McMaster University Osteoarthritis Index scores (mean difference 1.44 [95% CI 0.71 to 2.17]). Tests of subgroup differences revealed few differences in treatment estimates by study design, though observational studies had greater statistical power and thus demonstrated statistically significant findings more often. The certainty of the evidence for most outcomes was low-to-very low. Fixed-bearing implants may provide a significantly lower risk of revision and dislocation and improved function compared to mobile-bearing implants for unicompartmental knee arthroplasty patients. The lack of randomized trials limits the certainty of the evidence and remains a priority to confirm observational study findings.