Spinal cord potential recordings from the extradural space during scoliosis surgery

For monitoring spinal cord functions during corrective surgery of scoliosis, we have recorded percutaneously from the posterior extradural space at the C5-7 levels the ascending conducted spinal cord potentials (ASCP) in response to extradural stimulation of the cauda equina in 134 patients. The ASCP consists of three spike-like components (C1, C2 and C3) followed by slow components. The extradurally recorded ASCP were not affected by anaesthetic agents. There were no significant differential effects of spinal distractions on each of the three spike potentials. There were no post-operative neurological abnormalities in patients whose ASCP showed no changes, amplitude increases, amplitude decreases of less than 50% or latency increases (> 0.2 ms) during spinal manipulations (no false negatives, but some false positives). Five patients who suffered postoperative neurological damage exhibited more than 50% changes in amplitude of the ASCP during surgery. All these neurological sequelae occurred in the first 80 patients. In the last 54 patients, in whom the distraction forces on the spine were controlled rapidly by observation of the amplitude changes in ASCP, there were no postoperative 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 immediately when the amplitudes of the ASCP decrease by more than 50% of control values with or without latency increases.