Does the use of muscle relaxants during anaesthesia for hip arthroscopies influence the pressure on the perineum?

Many types of surgery, such as some types of hip replacement surgery, hip arthroscopies or the re-alignment of femoral fractures need to be performed on a traction table. In order to not pull the patient off the operating table when pulling on the leg, a padded perineal post is used. However, once traction is applied, the patient’s pudendal nerve region is pressurized by the post and the nerve can subsequently be damaged. This can result in significant nerve dysfunction which may be short-lived, but can also last for years after surgery. Sexual dysfunction after operations on a traction table is a long-known, but difficult to avoid problem (1-3). Mallet et al.(1) studied 168 patients after either operations on a traction table or a normal (non-traction) operating table. They found a 40.5% rate of erectile dysfunction (ED) in otherwise young, healthy males even years after operations on a traction table. Investigating potential influencing factors, the dose of the muscle relaxant administered during the anaesthetic was the only modifiable factor, with higher doses likely to prevent ED. The authors concluded that good relaxation leading to lower traction forces required and consequentially lower pressures on the pudendal nerve explained the superior outcome after deeper muscle relaxation (1). Though this theory seems logical, it has actually never been proven. Aim of this study is to determine the effect of deep muscle relaxation on the pressure on the perineum by the perineal post during operations on a traction table. Using an ultra-thin (approx.1 mm) pressure sensor foil embedded into the perineal post, we propose to measure the changes in pressures on the pudendal nerve after muscle relaxation. Fourty patients scheduled for elective hip arthroscopic surgery at Joondalup Health Campus and Glengarry Private Hospital will be included in this study. All patients will receive a standard general anaesthetic. After traction is applied on the operated leg, the resulting pressure on the perineum will be recorded. With the applied traction unchanged, the patient then receives a dose of the muscle relaxant rocuronium and the resulting change in pressure will be monitored. This concludes the study. The proposed project will close a significant gap of knowledge and, in a simple and risk-free approach, may lead to a change in anaesthesia practice. In addition, the joint width (hip) wil be measured before and after apralysis using portable xrays. If the joint width increases after the paralysis, the traction on the patients's leg will be reduced until the joint width is back to pre-paralysis status. At this stage the pressure on the pudendal nerve will be recorded again. References 1. Mallet R, et al. Urology. 2005;65(3):559-63. 2. Brumback RJ, et al. The Journal of bone and joint surgery American volume. 1992;74(10):1450-5. 3. Chan PT, et al.The Journal of trauma. 1999