 With the assumption that the difference in the VAS score at the 5th min between the two surgical techniques being 1 and the expected standard deviation for two groups being 0.9, it was estimated to include 20 patients in the groups for which the least difference was expected. The statistical significance level was calculated as 0.015 owing to the presence of 3 groups and with the prediction that repeated measurement analysis would be performed assuming that the Bonferroni correction would be used. The power of the present study was 80 with these calculations. 