The impact of neuromuscular blocking agents on traction forces during total hip replacement surgery

Orthopaedic surgeons frequently claim that the administration of muscle relaxants (NMBA) in patients under general anaesthesia facilitate surgery, especially when significant forces may be required (e.g. dislocation of hip joint, femoral realignment during operation of femoral fractures). However, despite the fact that NMBA are frequently used during general anaesthesia for orthopaedic surgery, no evidence for their benefit on operating conditions exists. Therefore, this trial aims to investigate the influence of NMBA on traction forces during hip replacement surgery. 20 Patients scheduled for hip replacement surgery under general anaesthesia will be included in this trial. Patients will receive a standard general anaesthetic. Patients for this form of hip replacement surgery are generally operated on a special operating table with the patients feet placed in shoe-like brackets. This allows the application of significant tension and torque to the patients operated leg in order to enable the surgical preparation of the hip joint for the prosthesis. With the help of a measurement instrument (Newton Meter installed within the traction mechanic of the operating table) we will measure the forces required to extend a patient's leg to facilitate surgery. Thereafter, an NMBA (rocuronium = most often used NMBA at RPH) will be slowly administered to finally achieve muscle paralysis. During the time of paralysis development, traction forces on the leg will be measured. Aim is to investigate whether NMBA can significantly reduce the forces required during hip replacement surgery.