Comparison of survival rate and risk of revision for mobile-bearing and fixed-bearing total knee replacements.

Objectives: This study aims to determine whether there is a difference in the rate of survival and risk of revision for mobile-bearing (MB) compared with fixed-bearing (FB) total knee replacements (TKRs).

Patients and methods: This prospective observational study included 1,571 cemented non-posterior-stabilized TKRs without patellar resurfacing with the subsequent revision surgery in 63 patients (23 males, 40 females; mean age 69.7 years; range, 46.5 to 85.5 years). The group of FB TKRs consisted of 756 non-revised and 31 revised implants. The group of MB TKRs included 752 non-revised and 32 revised knees. We determined the survival rate of TKR with Kaplan-Meier method and the relative risk (RR) of the revision in relation to the type of the insert. The analysis of the RR was divided into subgroups based on the time to revision and the reason for revision.

Results: No significant difference was found between FB and MB TKRs regarding the cumulative survival rate and the RR of total revision for any reasons. In the subgroup of early revisions for any reason, 2.22-fold increased risk of revision was found in the MB (p=0.02). The risk of late revisions for any reason in MB was lower than the risk in FB (RR 0.27; p=0.009). Higher risk of revision for instability was found in the subgroup of early revisions in MB (RR 23.8; p=0.03). MB was associated with significantly lower risk of total (RR 0.46; p=0.049) and late revisions for aseptic loosening (RR 0.14; p=0.008).

Conclusion: No differences were found in the cumulative survival rates between MB and FB TKRs. MB TKRs were associated with a lower risk of revision due to aseptic loosening in comparison with FB TKRs. MB inserts represented a significant risk factor only for early revisions due to instability.