Loss of spinal cord monitoring signals in children during thoracic kyphosis correction with spinal osteotomy - Why does it occur and what should you do?

Study Design. A retrospective review of pediatric kyphosis patients undergoing a spinal cord-level osteotomy for correction. Objective. To evaluate the prevalence, etiology, timing, and intervention related to loss of spinal cord monitoring data during surgical correction of pediatric kyphosis in the spinal cord region. Summary of Background Data. Although much has been written regarding the risks inherent to scoliosis surgery, there is less literature available regarding the neurologic outcomes of pediatric kyphosis surgery. As more surgeons contemplate posterior-only kyphosis correction with spinal cord-level osteotomies, the importance of maintaining spinal cord neurologic function is paramount. Methods. Forty-two patients with pediatric kyphosis undergoing a posterior-only spinal reconstruction with a spinal cord level osteotomy or posterior-based vertebral column resection performed were reviewed. Patients were categorized by diagnosis, type and incidence of osteotomies, and loss of neurogenic mixed-evoked potential (NMEP) data. Interventions required to regain data and postoperative neurologic outcomes were also reviewed. Results. Of the 42 patients, 9 (21.4%) demonstrated a complete loss of NMEP data sometime during surgery while concomitant somatosensory sensory-evoked potentials (SSEP) remained within acceptable limits of baseline values. All 9 patients had intraoperative intervention including: blood pressure elevation (n = 1), release of corrective forces (n = 2), blood pressure elevation and correction release (n = 3), malalignment/ subluxation adjustment (n = 1), further bony decompression (n = 1), or restoration of anterior column height via a titanium cage along with further posterior decompression (n = 1). In all cases, SSEPs were unchanged and NMEPs returned varying from 8 to 20 minutes after loss, with all patients having a normal wake-up test intraoperatively and a normal neurologic examination after surgery. Conclusion. Intraoperative multimodality monitoring with some form of motor tract assessment is a fundamental component of kyphosis correction surgery in the spinal cord region in order to create a safer, optimal environment and to minimize neurologic deficit. The surgeon must be able to trust the information monitoring provides and act on it accordingly.