SPINAL-CORD POTENTIAL RECORDINGS FROM THE EXTRADURAL SPACE DURING SCOLIOSIS SURGERY

For monitoring spinal cord functions during corrective surgery of scol iosis, we have recorded percutaneously from the posterior extradural s pace at the C5-7 levels the ascending conducted spinal cord potentials (ASCP) in response to extradural stimulation of the cauda equina in 1 34 patients. The ASCP consists of three spike-like components (C1, C2 and C3) followed by slow components. The extradurally recorded ASCP we re not affected by anaesthetic agents. There were no significant diffe rential effects of spinal distractions on each of the three spike pote ntials. There were no postoperative neurological abnormalities in pati ents whose ASCP showed no changes, amplitude increases, amplitude decr eases of less than 50% or latency increases (> 0.2 ms) during spinal m anipulations (no false negatives, but some false positives). Five pati ents who suffered postoperative neurological damage exhibited more tha n 50% changes in amplitude of the ASCP during surgery. All these neuro logical sequelae occurred in the first 80 patients. In the last 54 pat ients, in whom the distraction forces on the spine were controlled rap idly by observation of the amplitude changes in ASCP, there were no po stoperative neurological abnormalities, except for one patient in whom an accidental spinal cord injury was produced by a hook. The results suggest that the distraction force on the spine must be reduced immedi ately when the amplitudes of the ASCP decrease by more than 50% of con trol values with or without latency increases.