Sample size and power considerations
The sample size for this trial is based on an expected mean difference between groups of HHS. We used the HHS 3-month after THA increased ≥ 2 as effective, with a standard deviation (SD) of 3 according to our clinical experience. The error was set at 0.05 and the power level at 90%, a minimum of 49 patients per group was needed. This minimal sample size estimate has been increased by 20% after considering the potential dropouts, finally including 59 patients for each group.