Survivorship of fixed vs mobile bearing unicompartmental knee replacement: A systematic review and meta-analysis of sixty-four studies and National Joint Registries

Background: Unicompartmental knee replacement (UKR) prostheses can use fixed (FB) or mobile bearing (MB) constructs. We compared survivorship and failure modes of both designs. Methods: The inclusion criteria were studies published between 2005 and 2020 with minimum average follow-up of five years reporting the survival andior number of revisions of specific designs in medial and lateral UKRs. Pooled rate of revision per 100 patient years (PTIR) was estimated using a random effects model. Results: Seventy cohorts of 17,405 UKRs with weighted mean follow-up of 7.3 years (0.1-29.4 years) were included. A total of 170,923 UKRs were identified in registry reports at a weighted mean implant survival time of 15.4 years. PTIR in MB UKR versus FB UKR was similar [1.45 vs 1.40, (p = 0.8)]. In cohort studies, the overall PTIR for MB was also similar to 113 [1.03 vs 0.78, (p = 0.1)]. For medial UKR, the PTIR for MB was marginally greater but not significantly different to FB [0.96 vs 0.81, (p = 03)], whilst for lateral UKR, the PTIR for MB was significantly worse than for 113 [2.20 vs 0.72, (p < 0.01)]. Polyethylene wear is more common in 113 implants, whilst MB implants are revised more often for bearing dislocation. Conclusions: Overall implant survival in mid- to long-term studies is similar for MB versus FB medial UKRs. MB have a four-fold higher risk of revision in comparison to FB when used for lateral UKR. Crown Copyright (C) 2020 Published by Elsevier B.V. All rights reserved.