Statistical Analysis and Sample Size
The sample size calculation was performed in relation to the difference in the postoperative decrease in Hb level among the 3 groups using G*Power Version 3.1.7 (Franz Faul; UniKiel, Germany) software. On the basis of our preliminary data of 60 patients who underwent primary total knee arthroplasty and were assessed for the same measure, the mean decrease in Hb level (and standard deviation) was 39.3 ± 5.89 g/dL. A reduction of 10% (4 g/dL) in Hb level in patients who received a daily dose of 10,000 IU from preoperative day 5 to postoperative day 3 was recorded as a significant difference. In summary, 60 patients per arm were needed, with a power of 0.90 and a significance level of 0.05.
We compared the quantitative data between groups using 1-way analysis of variance and Tukey’s post hoc test. The Pearson chi-square test or Fisher’s exact test was used to analyse qualitative comparative parameters. All analyses were performed using SPSS for Windows, Version 19.0 (SPSS Inc, Chicago, IL). Significance was set at P < 0.05.