Purpose: A concern that arises with any new prosthesis is whether it will achieve satisfactory long-term implant stability. The gold standard of assessing the quality of fixation in a new or relatively new implant is to undertake a randomized controlled trial using radiostereometric analysis. It was hypothesized that both mobile-bearing total knee arthroplasty and fixed-bearing total knee arthroplasty have comparable migration patterns at 2-year follow-up. This study investigated two types of cemented total knee arthroplasty, the mobile- or fixed-bearing variant from the same family with use of radiostereometric analysis.Methods: This prospective, patient-blinded, randomized, controlled trial was designed to investigate early migration of the tibia component after two years of follow-up with use of radiostereometric analysis. A total of 50 patients were randomized to receive a mobile- or fixed-bearing TKA from the same family. Patients were evaluated during 2-year follow-up, including radiostereometric analysis, physical and clinical examination and patient reported outcome measures (PROMs).Results: At two-year follow-up, the mean (±SD) maximum total point motion (MTPM) in the fixed-bearing group was 0.82 (±1.16) versus 0.92 mm (±0.64) in the mobile-bearing group (p = n.s) with the largest migration seen during the first 6 weeks (0.45 ± 0.32 vs. 0.54 ± 0.30). The clinical outcome and PROMs significantly improved within each group, not between both groups.Conclusions: Measuring early micromotion is useful for predicting clinical loosening that can lead to revision. The results of this study demonstrate that early migration of the mobile-bearing is similar to that of the fixed-bearing component at two years and was mainly seen in the first weeks after implantation.Level Of Evidence: Randomized, single-blind, controlled trial, Level I. [ABSTRACT FROM AUTHOR]