Deep neuromuscular paralysis during hip arthroscopic surgery: influence on perineal tissue pressures and hip joint width

Pudendal nerve injuries are not an uncommon side effect of patient positioning on a traction table, and muscle relaxation has been suggested to mitigate this risk by reducing pressure on the perineum. A total of 40 patients scheduled for hip arthroscopic surgery under general anaesthesia were recruited. After induction of anaesthesia, pressures on the perineum were measured in 20 subjects by means of an ultra-thin pressure sensor mat wrapped around the perineal post. Perineal pressures were assessed after the induction of anaesthesia, after leg traction and after deep muscle relaxation. In 22 subjects, the hip joint width was measured radiographically at the same time points. Pressures on the perineum were high after traction (median maximum pressure 2540 g cm(−2)). Neuromuscular paralysis reduced perineal pressures only minimally, but significantly (−5 g cm(−2); P = 0.007). Traction increased hip joint width significantly [mean 66 (12)%; P = 0.001) and muscle relaxation further increased joint width by a mean of 3.2 (0–20)% (P = 0.001). Muscle relaxation was more beneficial for male patients (joint width increase 6.8% versus 2.8%; P = 0.04), as well as patients in whom traction alone did not achieve sufficient joint width. Muscle relaxation reduced the perineal pressure during hip arthroscopic surgery by only a negligible amount. With regard to joint space, relaxation may be of highest benefit in male patients and/or patients in whom traction alone produces only a relatively small increase in joint width (trial registration: ANZCTR 12617000191392).