SOMATOSENSORY EVOKED POTENTIAL SPINAL CORD MONITORING IN ANTERIOR DEFORMITY SURGERY – IS IT USEFUL?

Abstract

Objective To assess the validity of Somatosensory Evoked Potential (SSEP) monitoring in identifying potential spinal cord vascular damage resulting from segmental artery ligation in anterior spinal deformity correction.

Design SSEP monitoring was undertaken in patients deemed at risk of spinal cord vascular injury during corrective surgery. The segmental vessels of the vertebral bodies to be instrumented were identified. Baseline SSEPs were obtained prior to application of non-crushing microvascular clamps. After ten minutes of occlusion, further SSEP recordings were made. Surgery proceeded with either, vessel ligation and division allowing anterior instrumentation, or vessel sparing anterior release.

Subjects 22 patients were included; 7 had Scheuermann’s hyperkyphosis and 15 had scoliosis (11 idiopathic, 3 syndromic, 1 neuromuscular). Perceived risk was defined by the presence of hyperkyphosis, abnormal neurological examination or radiologically identified spinal cord anomaly.

Outcome Measures A drop of 30% from baseline reading was taken as significant. Post-operative neurological outcome was correlated with intra-operative signal change and alteration in planned surgery.

Results There was no significant drop in post-clamping SSEPs in the hyperkyphotic patients. In 3 scoliosis patients anterior instrumentation was abandoned and a release was performed. Staged posterior instrumentation followed. In a further 2, anterior instrumentation proceeded but in a modified fashion. The remaining 10 patients had no significant drop and underwent the surgery as planned. No patient sustained a neurological injury.

Conclusions SSEP monitoring is safe in assessing the apparent contribution of segmental vessel blood supply to the spinal cord in spinal deformity surgery. It has allowed timely alteration of planned surgical procedures that potentially may have caused vascular spinal cord injury.