Evaluation of Intrapedicular Screw Position Using Intraoperative Evoked Electromyography

Abstract

This study analyzed the parameters needed for electrical stimulation of vertebral pedicle drill bits and screws. The feasibility of using electrically evoked electromyography was studied. Considerable potential for damage of adjacent nerve roots with incorrectly placed bits and screws exists with pedicular fixation of the lumbar spine. Ninety-five drill bits, one hundred forty-four screws, and thirty-four exposed nerve roots were electrically stimulated in thirty-six patients. Simultaneous evoked electromyographic activity was recorded from four muscle groups in each lower extremity during partial neuromuscular blockade. A constant current threshold of 6 mA or less correlated with misplaced drill bits and screws that broached the cortex. Evoked electromyography was 93% sensitive whereas radiography was only 63% sensitive to detecting bits and screws that had broached the cortex. Evoked electromyography is a valuable sensitive adjunct to radiographic examination of pedicle drill bit and screw placement.