Monopolar-probe monitoring during spinal surgery with expandable prosthetic ribs

Intraoperative monitoring (IOM) has been proven to decrease the risk of neurological injury during scoliosis surgery. The vertical expandable prosthetic titanium rib (VEPTR) is a device that allows spinal growth. However, injuries to the spinal cord and brachial plexus have been reported after VEPTR implantation in 2 and 5% of patients, respectively. Simultaneous monitoring of these two structures requires the use of multiple time-consuming and complex methods that are ill-suited to the requirements of paediatric surgery, particularly when repeated VEPTR lengthening procedures are needed. We developed a monopolar stimulation method derived from Owen's monitoring technique. This method is easy to implement, requires only widely available equipment, and allows concomitant monitoring of the spinal cord and brachial plexus. The primary objective of this study was to assess the reliability of our technique for brachial plexus monitoring by comparing the stability of neurogenic mixed evoked potentials (NMEPs) at the upper and lower limbs.

We hypothesised that the coefficients of variation (CVs) of NMEPs were the same at the upper and lower limbs.

Twelve VEPTR procedures performed in 6 patients between 1st January 2012 and 1st September 2014 were monitored using a monopolar stimulating probe. NMEPs were recorded simultaneously at the upper and lower limbs, at intervals of 150 s. The recording sites were the elbow over the ulnar nerve and the popliteal fossa near the sciatic nerve. Wilcoxon's test for paired data was used to compare CVs of the upper and lower limb NMEPs on the same side.

Mean CV of NMEP amplitude at the lower limbs was 16.34% on the right and 16.67% on the left; corresponding values for the upper limbs were 18.30 and 19.75%, respectively. Mean CVs of NMEP latencies at the lower limbs were 1.31% on the right and 1.19% on the left; corresponding values for the upper limbs were 1.96 and 1.73%. The risk of type I error for a significant difference between the upper and lower limbs was 0.5843 on the right and 0.7312 on the left for NMEP amplitudes and 0.7618 on the right and 0.4987 on the left for NMEP latencies.

Using an epidural active electrode and a sternal return electrode allows simultaneous stimulation of the cervical spinal cord and brachial plexus roots. The NMEPs thus obtained are as stable (reliable) at the upper limbs as at the lower limbs. This easy-to-implement method allows simultaneous monitoring of the upper and lower limbs. It seems well suited to VEPTR procedures.

IV, retrospective single-centre non-randomised study.