Intra-Operative Somatosensory-Evoked Potential Monitoring

Purpose. To evaluate the usefulness of intra-operative somatosensory-evoked potentials (SSEPs) in monitoring spinal cord status via the posterior tibial nerve. Methods. 84 men and 28 women aged 16 to 66 years (72% were aged 20 to 40 years) with spinal trauma (63 in the lumbar and 49 in the thoracic spine) underwent posterior instrumentation and fusion using bone grafts. All 63 patients with lumbar spinal injury and 35 of the patients with thoracic spinal injury were treated with pedicular screws. The remaining 14 patients had their thoracic spinal injury fixed with sublaminar wires. Cortical scalp recordings were used. Baseline tracings were obtained prior to surgical intervention and after establishment of anaesthesia. If changes persisted for more than 15 to 20 minutes or if they did not show definite signs of resolution, event reversal was considered. Results. Of the 112 patients, 74 (66%) had no changes in Cz-Fpz patterns and neurological status, whereas 14 (13%) showed improved patterns (2 of them had the same neurological status postoperatively) and 24 (21%) displayed deteriorated patterns prompting intervention. Of the 24 patients prompting intervention, 20 improved substantially (19 had no new neurological deficits and one had deteriorated neurological status) and 4 improved minimally (2 had no new deficit and 2 had new deficits), with 88% sensitivity and 78% specificity. 15 patients were true-positives with an identifiable cause; 21 were false-positives with no neurological deterioration or recognisable cause. Conclusion. Intra-operative SSEP monitoring helps identify acute neurological and systemic (hypoxia or hypotension) impairment and enables prompt correction. This makes surgery available to high-risk patients and enables surgeons to carry out more extensive procedures. It also provides valuable documentation in the event of medico-legal dispute.