Risk of sciatic nerve traction injury during hip arthroscopy­is it the amount or duration? An intraoperative nerve monitoring study.

BACKGROUND: Using intraoperative nerve monitoring we prospectively studied the prevalence, pattern, and predisposing factors for sciatic nerve traction injury during hip arthroscopy. METHODS: The transcranial motor (tcMEP) and/or somatosensory (SSEP) evoked potentials of seventy-six patients undergoing hip arthroscopy in the lateral position were recorded. Changes in the posterior tibial and common peroneal nerves were evaluated to assess the effects of the amount and duration of traction on nerve function. Sixteen subjects were excluded because of incomplete data. Nerve dysfunction was defined as a 50% reduction in the amplitude of SSEPs or tcMEPs or a 10% increase in the latency of the SSEPs; nerve injury was defined as a clinically apparent sensory or motor deficit. Traction time and weight were continuously monitored with use of a custom foot-plate tensiometer. RESULTS: Of sixty patients (thirty-one female and twenty-nine male, with a mean age of thirty-seven years [range, sixteen to sixty-one years]), thirty-five (58%) had intraoperative nerve dysfunction and four (7%) sustained a clinical nerve injury. The average maximum traction weight (and standard deviation) for patients who did and those who did not have nerve dysfunction or injury was 38.1 ± 7.8 kg (range, 22.7 to 56.7 kg) and 32.9 ± 7.9 kg (range, 22.7 to 45.4 kg), respectively. The odds of a nerve event increased 4% with every 0.45-kg (1-lb) increase in the traction amount (age/sex-adjusted; p=0.043; odds ratio, 1.04; 95% confidence interval, 1.01 to 1.08). The average total traction time for patients who did and those who did not have nerve dysfunction was 95.9 ± 41.9 minutes (range, forty-two to 240 minutes) and 82.3 ± 35.4 minutes (range, thirty-eight to 160 minutes), respectively, and an increase in traction time did not increase the odds of a nerve event (p = 0.201). Age and sex were not significant risk factors. CONCLUSIONS: The prevalence of nerve changes seen with monitoring of SSEPs and tcMEPs is greater than what is clinically identified. The maximum traction weight, not the total traction time, is the greatest risk factor for sciatic nerve dysfunction during hip arthroscopy. This study did not identify a discrete threshold of traction weight or traction time that increased the odds of nerve dysfunction.

Intraoperative monitoring of facial and cochlear nerves during acoustic neuroma surgery. 1992.

Preservation of facial nerve function during acoustic neuroma surgery can be improved significantly by monitoring of facial electromyography (EMG) during surgery. Mechanical trauma during dissection causes EMG activity that can be played over a loudspeaker for direct feedback to the surgeon. Electrical stimulation can be used to locate the nerve even when it is out of direct view, and the threshold for stimulation provides a measure of facial (or other motor nerve) integrity. Cochlear nerve function also can be monitored by the recording of auditory brain stem responses or compound action potentials from an electrode placed on the nerve at the brain stem root entry zone.