Power calculations is based on the assumption of 75% response rate (0.75x30.000)= 22.500. Of these approximately 15% TEP=3375. Of TEP approximately 50% is done bilaterally, which is excluded from this study. Assuming a difference in pain of 4% in favor of TEP, it is needed more than 1200 patients in the TEP group to detect these differences, considered clinically meaningful.