Monitoring of the motor pathway during spinal surgery

Paraplegia caused by irreversible lesions of the spinal cord is one of the major possible complications after scoliosis surgery. Several monitoring methods have been proposed but none are completely satisfactory. Since 1986 the authors assessed motor pathways during scoliosis surgery, using electrical stimulation of the motor cortex and lower limb muscle recordings (tibialis anterior muscle). Twenty-seven patients were included in this study: 25 with idiopathic scoliosis and 2 with dorsal kyphosis. Recordings in anesthetized patients with hypothermia were performed before and after spinal derotation during the surgical procedure. Magnetic cortical stimulation was carried out in ten awake patients before and after surgery. Reproducible responses were obtained in 22 patients under anesthesia. In eight patients no difference of the latency of the muscle response was detected before and after the correction of the spinal angulation. In 14 patients the increase of latency ranged from 0.4 ms to 5.2 ms. No correlation was found between the slowing of motor conduction and the magnitude of spine correction. No central neurologic complications were seen after surgery. The authors concluded that their study demonstrated that motor pathway assessment in anesthetized patients can be performed at different times during the surgical procedure. This technique should help in the future monitoring spinal function during scoliosis surgery.