Unicompartmental knee replacement (UKR) prostheses can use fixed (FB) or mobile bearing (MB) constructs. We compared survivorship and failure modes of both designs.
The inclusion criteria were studies published between 2005 and 2020 with minimum average follow-up of five years reporting the survival and/or 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.
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 FB [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 = 0.3)], whilst for lateral UKR, the PTIR for MB was significantly worse than for FB [2.20 vs 0.72, (p < 0.01)]. Polyethylene wear is more common in FB implants, whilst MB implants are revised more often for bearing dislocation.
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.