No long-term difference between fixed and mobile medial unicompartmental arthroplasty.

BACKGROUND: Early studies in the literature reported relatively high early minor reintervention rate for the mobile-bearing unilateral knee arthroplasty (UKA) compared with short- and midterm survivorship after fixed- or mobile-bearing UKA. However, whether the long-term function and survivorship are similar is unclear.

QUESTIONS/PURPOSES: We therefore asked whether (1) mobile- or fixed-bearing UKAs have comparable function (as measured by the Knee Society scores); (2) mobile- and fixed-bearing UKA have comparable Knee Society radiographic scores; and (3) the long-term survivorship is comparable.

METHODS: We retrospectively reviewed 75 patients (79 knees) with a fixed-bearing UKA and 72 patients (77 knees) with a mobile-bearing UKA operated on between 1989 and 1992. Mean age of the patients was 63 years; gender and body mass index (26 kg/m(2)) were comparable in the two groups. We obtained Knee Society function and radiographic scores and determined survival. The minimum followup was 15 years (mean, 17.2 ± 4.8 years; range, 15-21.2 years).

RESULTS: The mean Knee Society function and knee scores were comparable in the two groups. Radiographically, the number of overcorrections and the number of radiolucencies were statistically higher in the mobile-bearing group (69% versus 24%). At final followup, considering revision for any reason, 12 of 77 (15%) UKAs were revised (for aseptic loosening, dislocation, and arthritis progression) in the mobile-bearing group and 10 of 79 (12%) in the fixed-bearing group (for wear and arthritis progression).

CONCLUSIONS: This long-term study did not demonstrate any difference in survivorship between fixed and mobile-bearing but pointed out specific modes of failure.