Purpose: The risk of injuring the radial nerves during spine instrumentation to correct spinal deformity is well known and accounts for about 50% of the neurological complications associated with this type of surgery. We describe a technique for monitoring the nerve roots during spinal surgery. Radicular monitoring was described by Hormes in 1993.
Material and methods: We report a retrospective analysis of 73 procedures for spinal deformity during which the nerve roots were monitored. The series included 27 men and 46 women, mean age 23.9 years (range 4.5–74.9). Forty patients were less than 18 years old. Procedures included posterior arthrodesis (n=65) and anterior arthrodesis (n=8). Indications were: idiopathic scoliosis (n=32), neurological scoliosis (n=21), congenital scoliosis (n=4), spondylolisthesis (n=2) and kyphosis (n=3). The study group included 68 patients (168 roots) with recordings obtained under the required conditions. The routine procedure involved permanent electrophysiological monitoring of muscle activity with a multi-channel electromyograph. We used microwires implanted within the muscle itself for electrodes. Target muscles depended on the position of the planned implants and the topography of the roots likely to be endangered during the surgical procedure or instrumentation. Explored roots were: T12 (n=9), L1 (n=24, L2 (n=40), L3 (n=24), L4 (n=23), L5 (n=11), S1 (n=22). Monitoring prohibited use of curare during anaesthesia.
Results: Prior to radicular monitoring, we had had two root injuries (T12 and L3) which resolved spontaneous (n=139). During the study, changes in the radicular signal were observed in seven patients. All signal anomalies triggered a modification of the surgical procedure and no postoperative deficit was observed. Incidents observed concerned congenital scoliosis (n=2), neurological scoliosis (n=2), and idiopathic scoliosis (n=3). Roots involved were L1 (n=1), L2 (n=2), L3 (n=2), L4 (n= 4), i.e. 11/163.
Discussion: Continuous intraoperative monitoring of the spinal roots exposed to surgery for spinal deformity enabled us to identify eleven cases of root suffering among 163 recordings. This permanent monitoring system enabled us to immediately modify the surgical procedure and to control and conflict between the instrumentation and the roots or possible stretching during the correction. This technique requires permanent monitoring during the spinal procedure to avoid false negatives. Curare cannot be used.
Conclusion: Intraoperative radicular monitoring is an effective way to avoid radicular complications of this type of surgery. The technique is sensitive and allows immediate adaptation of the surgical procedure. It requires close collaboration between the neurophysiologist, the orthopaedic surgeon and the anaesthesiologist.
