 Sample size and statistics: The sample size was calculated based on the distribution and variance of the primary outcome, i.e. the number of osteoclasts generated in vitro. From a population of 51 normal donors in our laboratory the number of osteoclasts generated was 601.1 156.8 osteoclastswell data presented at the 2007 annual meeting of the Canadian Rheumatology Association, in press at the Journal of Rheumatology. We considered a test significance level of 5 α 0.05 and the power of 80 to detect a difference of at least 100 osteoclastswell between the groups paired two-tailed t-test, which led to a total of 22 patients. Considering a 10 loss due to technical reasons the sample size was established at 25 patients. 