Effect of Tibial Component Overhang on Survivorship in Medial Mobile-Bearing Unicompartmental Knee Arthroplasty.

Background: Some studies have shown that the position of the tibial component in Oxford unicompartmental knee arthroplasty with a mobile bearing will affect the clinical outcome of patients. Hence, our study aimed to investigate the relationship between the overhang distance of the tibial component and the survival of the implant.Methods: A retrospective analysis of patients who underwent unicompartmental knee arthroplasty at the same institution from 2014 to 2018 was presented. The study was divided into three groups: minor underhang group (underhang between-3 and 0 mm); minor overhang group (overhang 0-3 mm); and major overhang group (overhang >= 3 mm). Demographic and clinical profile characteristics of each group were compared, and survival curves of each group were also compared using Kaplan-Meier and modeled using multivariate Cox regression.Results: A total of 351 knees were included in this study with a minimum follow up of three years and a mean follow up of 4.8 +/- 1.5 years. The revision rates in each group were 3.6% (minor underhang group), 2.7% (minor overhang group), and 20.9% (major overhang group) (P < 0.001). From the three groups' cumulative survival rates, the major overhang group was significantly lower than the other two groups (log rank P < 0.001). Multivariate Cox regression showed an association between the major overhang group and implant survival rate (hazard ratio = 7.515, 95% confidence interval = 2.500-22.593, P < 0.001)Conclusion: The risk of revision will increase if the tibial component overhangs more than 3 mm medially. Moreover, the reasons for revision are generally bearing dislocation and aseptic loosening.(c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).