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Background: Uncemented tibial components of total knee replacements have lower survival rates than cemented components. Radiostereometric analysis is a highly accurate, effective tool for investigating new implant designs. The purpose of this study was to compare an uncemented Trabecular Metal tibial component with a conventional cemented stemmed tibial component of the same design.Methods: Seventy subjects undergoing total knee replacement were randomized to receive either the Trabecular Metal or the cemented tibial component. Radiostereometric analysis of micromotion of the tibial components was performed postoperatively at six, twelve, and twenty-four months, and the maximum total point motion of the implant and three-dimensional translations and rotations were recorded.Results: Follow-up was complete for twenty-eight subjects in the Trabecular Metal group and twenty-one subjects in the cemented group. A subset of the Trabecular Metal components migrated extensively in the postoperative period, but all stabilized by one year and the proportion considered to be at risk for early aseptic loosening was 0.0 (95% confidence interval, 0.0 to 0.12) in the group as a whole. Four cemented components were considered to be at risk for early aseptic loosening (proportion at risk, 0.19; 95% confidence interval, 0.08 to 0.4).Conclusions: This study suggests that the Trabecular Metal component may be an effective alternative to the standard cemented tibial component.Level of Evidence: Therapeutic Level I. See Instructions to Authors for a complete description of levels of evidence.