Spinal cord monitoring during spinal surgery using somatosensory spinal evoked potentials

Intraoperative monitoring of spinal cord function has been carried out in 59 patients during spinal instrumentation for scoliosis. Posterior tibial nerve stimulation in the popliteal space was performed and spinal evoked potentials from electrodes in the spinous processes observed. A rod artifact problem causing partial obliteration of the wave form can be minimized or eliminated by careful selection of the insertion of the fixation device. A drop in amplitude of the signal occurred in many of the tracings from control to distraction observations but did not result in neurologic deficit. One patient had a loss of the signal after maximum distraction with a Harrington rod and a return with release of distraction. This patient awoke with paralytic urinary bladder retention which resolved spontaneously but no other neurologic deficit. This method has been used for monitoring of spinal cord function during Harrington rod instrumentation, using both compression and distraction systems as well as Luque rod instrumentation. This method is safe, simple, and provides consistent and predictable wave forms; it appears to be reliable in indicating continuation of spinal cord function during the procedure.