Loss of Spinal Cord Monitoring Signals in Children during Thoracic Kyphosis Correction with Spinal Osteotomy: Why Does it Occur and What Should You Do?

Methods: 36 pediatric patients with useful lower extremity function underwent a corrective spinal osteotomy for rigid kyphosis at one institution. Diagnoses included Scheuermann's kyphosis (n=13), congenital kyphosis (n=5), hemivertebra (n=6), neuromuscular kyphosis (n=4), connective tissue disorders (n=3), neurofibromatosis (n=2), and miscellaneous (n=3). All osteotomies performed were at the spinal cord level, which included vertebral column resection (n=6), posterior hemivertebra excision (n=6), pedicle subtraction osteotomy (n=3), and multiple Smith-Petersen osteotomies (n=21). Average preoperative kyphosis was 79º (range 32-140º) and the average correction was 37º (range 0-59º).

Results: There were seven cases (19%) of intraoperative NMEP loss. The signal loss occurred prior to any corrective maneuver (n=1), during corrective maneuvers (n=5), and 70 minutes after completion of correction (n=1). Correction of Scheuermann's kyphosis through multiple Smith-Petersen Osteotomies (5/14, 36%) and performance of a thoracic vertebral column resection (2/6, 33%) demonstrated the highest risk techniques for NMEP signal loss. With elevation of blood pressure (mean arterial pressure >80mmHg) and release of correction (see Figure), NMEP signals reappeared in all cases in an average 18 minutes (range 5-52), and surgery was successfully completed. Postoperatively, all patients had a normal neurological exam. A false negative NMEP response (undetected neurologic complication) occurred in one patient. The patient was treated by immediate rod removal and staged reinsertion without neurologic sequelae.

Conclusions: The incidence of intraoperative NMEP signal loss during spinal osteotomies for spinal cord level kyphosis correction in pediatric patients was 19%. Correction maneuvers combined with hypotension were the common etiologies. Reduction in the degree of kyphosis correction and blood pressure elevation reversed the signal loss in all cases. With early detection using NMEP monitoring, corrective action can be taken and neurologic injury avoided.

Hibbs Award Nominee for Best Clinical Paper