Limitations
Forty patients declined to participate in the study prior to randomization. The baseline characteristics of these patients are unknown, and potential selection bias cannot be ruled out. Eight patients were further lost to follow-up. The baseline characteristics of these patients did not differ from the included patients and therefore we believe that they did not bias the analysis. RSA is a precise and validated method to evaluate component migration patterns, but currently no thresholds for component migration have been established for the femoral components. However, when the migration pattern show stabilization for all patients with very low overall migration measures it can be taken as a positive indication of an expected good long-term fixation. As the observer was able to identify whether the components were cemented/cementless and single-peg/twin-peg, this study is only single-blinded. However, it seems unlikely that this would affect the results as the RSA analyses were conducted using automized RSA analysis software. Although this is a randomized study, the gender distribution was not comparable between the three groups, with relatively more female patients in the CSP group. We conducted sensitivity analyses to explore whether this was related to slightly lower component migrations in the CSP group, which was not found to be the case. Further, the BMD change over time was comparable between the male and the female cases, which leads us to believe that the migration results are not a result of the unbalanced sex distribution.