Objectives: Unicompartmental knee arthroplasty(UKA) has been more widely used for medial gonoarthritis. Recently used UKA implants include both fixed bearing (FB) and mobile-bearing (MB) designs. However, there has been little known regarding to which design provides superior long-term outcomes. The purpose of this study is to whether different bearing designs of UKAs induce differences in a long-term survival rate, failure mode and clinical outcomes.

Methods: We had performed 111 UKAs for medial gonoarthritis between 2002 and 2009, of which 44 knees had a MB design and 67 knees a FB design. 8 knees from MB design and 5 knees from FB design were lost during follow-up period. 2 patients from FB design expired. Patients with mobile-bearing UKA had a mean follow up of 8.3 year (range, 1-14.2 years); those with fixed-bearing UKA a mean follow up of 8.9 year (range, 1-14.1 years). Basic demographics between both groups did not show any differences. Patients were evaluated with clinical outcome scores using KOOS, revision rate and cause of revision.

Results: 5 of 36 (13.8%) MB knees were revised due to aseptic loosening, dislocation, and wear at a mean of 4.3 years, and 8 of 60 (13.3%) FB knees were revised due to aseptic loosening, infection, wear and arthritis progression at a mean of 7 years. Regarding to revision surgery as endpoint, the 7-year cumulative survival rates of the MB and FB designs were 0.917 (SE ± 0.0461) and 0.935 (SE ± 0.0312) and the 14-year cumulative survival rates 0.778 (SE ± 0.114) and 0.682 (SE ± 0.112), respectively. The differences in survival rates between MB and FB designs was not significant (log rank test p-value = 0.7287 at 7-years and p-value = 0.7886 at 14-years). The postoperative mean KOOS were comparable in the two groups.

Conclusions: This study showed that differences in survivorship and clinical outcomes between fixed and mobile bearing UKA did not demonstrate in a midterm and long-term follow up period. However, some causes of revision were different.