Role of intraoperative neurophysiological monitoring during spinal deformity surgery

Abstract

Background Because spinal surgery entails a risk of spinal cord injury, techniques to monitor spinal cord function intraoperatively have been developed. The main goal of such intraoperative neurophysiological monitoring (INM) is to permit identification of surgically induced neurophysiological changes so they can be corrected, thus avoiding postsurgical complications and permanent sequelae. Objective Evaluate the evidence in favor of implementing combined monitoring, using somatosensory evoked potentials (SSEP) and motor evoked potentials (MEP) for spinal surgery at the MUHC. Methods A literature review was conducted to identify studies that comprised at least 70 cases, of combined SSEP /MEP monitoring for spinal surgery published from 1995 to 2004. Results A total of 11 studies were identified meeting the inclusion criteria. No studies involved randomized comparisons, and all were simple case series. Despite this limitation, this literature gives ample evidence that INM allows potential intraoperative damage to the spinal cord to be identified rapidly and avoided through corrective action. Health Benefits Because the reported series vary greatly no precise estimate of the health benefits that might result from INM is possible. As a first approximation for the purpose of policy decisions, on the basis of the literature and reported present outcomes at the MUHC, it will be assumed that INM might prevent postoperative nerve deficit in approximately 3% of procedures, and might prevent severe and lasting deficits (eg. paraplegia) in 1% of procedures. Even nerve deficits that are not prevented are likely to be less severe as a consequence of the surgical adjustment resulting from monitoring. Furthermore, though this can also not be quantified, the assurance that monitoring gives to the surgeon is likely to result in more effective surgical procedures. Page 5 Economic issues Budget Impact It is estimated that approximately 100 surgical procedures per year require spinal monitoring at the MUHC at this time. Excluding all costs associated with the treatment of nerve deficits that might have been avoided by monitoring, and the costs of possible legal actions, it is estimated that to supply combined INM for 100 procedures per year at the MUHC would cost approximately $ 46 000. Cost Effectiveness Using the above assumptions it is reasonable to assume that the monitoring of 100 patients per year might prevent minor and transient postoperative lesions in two patients, and permanent serious defects in one patient per year. Ignoring the potentially very high costs that might be involved in the long-term care of patients with severe lesions, these health benefits could be achieved at the cost of approximately $ 46 000 the year to the MUHC. Conclusions There is good evidence to support the conclusion that intraoperative spinal monitoring during surgical procedures that involve risk of spinal cord injury is an effective procedure that is capable of substantially diminishing this risk. In the absence of any precise estimates it is reasonable, for the purpose of this decision, to assume that an expenditure of approximately $46,000 per year (or $460 per patient) might prevent one patient suffering serious permanent spinal cord injury and less serious complications or sequelae in approximately 2 other patients. Even if the cost of maintaining such patients is excluded, this is a highly acceptable cost to benefit ratio. A potential problem relating to the extension of combined SSEP / MEP monitoring to two MUHC sites is the relatively low rate of remuneration of the Neurophysiologists who play an essential role in this activity, and the resulting difficulty of recruitment Page 6 Recommendations It is recommended that the MUHC make available combined SSEP / MEP monitoring for all cases of spinal surgery for which there is a risk of spinal cord injury. Although professional remuneration is outside the hospitals responsibility, it is suggested that the MUHC, together with other institutions that undertake this form of monitoring, should consider drawing this problem to the attention of the FMSQ