A difference in bacterial quantity of a factor 10 (1.0 log10) between intervention and control group is judged to be of clinical significance in the development of SSI. To detect a difference of 1.0 log in bacterial quantity with a power level of 80%, a significance level of 5% and a standard deviation 1.0 log10, a sample size of 16 knees in each group is required, necessitating the inclusion of 16 patients . To recruit this number of patients, an inclusion period of 6 months is anticipated.