Cord monitoring changes and segmental vessel ligation in the "at risk" cord during anterior spinal deformity surgery.

STUDY
DESIGN: Retrospective analysis of all cases of anterior spinal deformity surgery that had intraoperative spinal cord monitoring (somatosensory-evoked potentials, SSEPs).
OBJECTIVES: The prime purpose of this study was to determine the incidence of significant SSEP changes in patients undergoing anterior spinal deformity surgery. A secondary objective was to ascertain if patients with "cords at risk" were more likely to produce significant intraoperative SSEP changes and what proportion of these changes resulted in postoperative neurological deficit. SUMMARY OF BACKGROUND DATA: There is anecdotal evidence to suggest that patients with intraspinal abnormalities are at greater risk of postoperative neurological deficit after spinal deformity surgery. To date, there have been no studies detailing this risk and how it relates to the type of surgery performed. This is a question of increasing relevance with the modern trend towards more anterior scoliosis correction and instrumentation. Recent reports have suggested a low incidence of neurological complication with anterior deformity procedures. There is controversy as to whether SSEP monitoring is required for these anterior procedures and whether soft clamping of segmental vessels before their division is a necessary precaution.
METHOD: This study is a chart review of all patients who had an anterior deformity operation between 1990 and 2001. Those patients who had a complete data set (preoperative magnetic resonance imaging scan, patient and procedural documentation, and adequate intraoperative SSEP traces) were included in this study. A significant SSEP change was correlated with the type of procedure performed, whether that patient had a "cord at risk" (CAR) and the degree of postoperative neurological deficit if present.
RESULTS: During the study period, 871 patients underwent elective anterior spinal deformity surgery. Ninety five (11%) patients had intraspinal abnormalities on magnetic resonance imaging. From this group, 27 (3%) were termed CAR. Twenty six (3%) patients had significant change in the intraoperative SSEP monitoring. Seventeen (2% total) occurred in the CAR group and nine (1% of total) in the normal cord group. There were five patients (0.6%) with significant postoperative neurological deficits, four (0.5%) in the CAR group, and one (0.1%) in the normal cord group. These patients had also demonstrated changes in their SSEPs. The sensitivity of SSEP monitoring for the whole series was 100%, specificity 97.5%, the positive predictive value was 19% and the negative predictive value was 100%. The CAR group was significantly more likely to have significant SSEP changes during any operation and was more likely to have postoperative paresis.
CONCLUSION: Patients with identified cords at risk should undergo spinal cord monitoring (SSEP) if they undergo anterior spinal deformity surgery. Soft clamping of segmental vessels is indicated with cord monitoring to prevent the risk of postoperative neurological sequelae.