The ultrasonic knife we have used in our study exploits the electrical impulses produced by a high-frequency ultrasound generator, transferred to a hand piece and converted into a mechanical movement at a frequency of 55.5 kHz (11,12) (Ultracision®, Ethicon Endo Surgery ). We have chosen this instrument because the relatively low temperatures generated in the process, ranging from 50 to 100 °C, result in a coagulative necrosis which allows both cutting and effective sealing of blood and lymphatic vessels, therefore preventing lymphatic leaks more effectively compared with conventional diathermy. The latter produces temperature up to 400 °C resulting in char formation and deleterious thermal effects to a distance of up to 1cm from the blade and extensive formation of necrotic tissue.

We have estimated Using the data of a previous unpublished pilot study, the sample size required for our trial using the data of a previous unpublished pilot study, indicating that to detect a significant difference in length of stay (delta = 4of four days, with a mean standard deviationsdigma of = 4.5 days, between the two groups with a level of significance of alpha = 5% and a power of1 - beta = 90%), we needed to enroll was estimated in 28 patients in each group arm. As a precaution we decided to increase the sample size by 25% to 35 patients per group arm, in case we needed to use non-parametric tests in subsequent statistical analysis. A total of 94 patients with operable breast carcinoma were recruited between January 2000 and December 2004: 1 male and 93 females (min 34, q1 58, median 65, mean 64.7, q3 73, max 95). All patients underwent total mastectomy or quadrantectomy and 1st or 2nd level axillary lymphadenectomy. Patients were randomly allocated to two treatment groups: patients allocated to Group A were operated on using exclusively the ultrasonic knife (Ultracision®, Ethicon Endo Surgery) for both the mastectomy or quadrantectomy and axillary dissection (38 cases, mean age of 64.6 years, min 34, q1 58, median 66, q3 70, max 95); patients allocated to Group B (control group) were operated on using a conventional diarthermy knife was (56 cases, mean age of 65.0 years,min 37, q1 59, median 65, q3 74, max 89). In all cases the type of a redon n°14 suction drain was left in the axillary cavity and removed as soon as the amount of fluid dropped to 35 ml/24h or less. The patient was discharged home the same day the drain was removed.

During the postoperative period the following data were collected: the total amount of fluid drained, the number of days the drain was leftof drainage, the length of post-operative stay, and early and late complications. Early complications were specifically recorded: wound seromas and hematomas, wound infections, necrosis of wound margins and period of time (in days) the seroma needed to be needle-aspirated following removal of the drain. Late complications recorded were lymphedema, strength and sensation deficits and chronic arm pain. A cost analysis was also done considering materials employed and length of hospital stay. Statistical analysis was done using open source "R" software, version 2.5.1 (18). The Shapiro-Wilk test was used to verify the normal distribution of data; heteroscedastic, normally distributed data were analysed using the F-test of variance; Student's t test was used for homoscedastic data. For non normally distributed data the non-parametric Wilcoxon-Mann-Whitney test was used. Survival analysis was analysed using Cox's regression model, in the hypothesis of proportional risk.