EVOKED AND SPONTANEOUS ELECTROMYOGRAPHY TO EVALUATE LUMBOSACRAL PEDICLE SCREW PLACEMENT

Study Design. A prospective study was performed to evaluate the effect iveness of evoked and spontaneous electromyography in predicting pedic le wall breakthrough and subsequent lumbar radiculopathy occurring aft er placement of pedicle screw instrumentation of the lumbar spine. Obj ectives. To correlate cortical breakthrough of the pedicle wall with a n electrically evoked electromyography threshold of stimulation, to as sess the sensitivity of mechanically evoked electromyography for nerve root irritation, and to correlate postoperative nerve root irritation with intraoperative findings. Summary of Background Data. Pedicle wal l breakthrough has been evaluated by radiographic means and found to b e difficult to evaluate. Methods to perform both electrically evoked a nd mechanically evoked electromyography have been developed more sensi tive tests for breakthrough. Methods. Twenty-five patients receiving 1 12 pedicle screws were evaluated. Results. Cortical breakthrough was a ssociated with electrically evoked electromyography threshold of less than 11 milliAmps. Not all screws that had broken through the pedicle wall caused a postoperative radiculopathy. Electromyographic activity was sensitive to nerve root stimulation. Conclusions. Measuring the el ectrically evoked electromyography threshold of stimulation helps to a ssess pedicle screw placement. Mechanically evoked electromyography in dicates intraoperative nerve root displacement. Postoperative radiculo pathy correlated with pedicle wall breakthrough, but did not occur in every case.