INFLUENCE OF RIGID SPINAL INSTRUMENTATION ON THE NEUROGENIC MOTOR EVOKED-POTENTIAL

Three case reports are presented to illustrate how placement of spinal instrumentation obliterates previously normal neurogenic motor evoked potentials (NMEPs) elicited by transosseous electrical stimulation. T his results in an unacceptably high false-positive rate for NMEP recor dings during scoliosis surgery. The loss of the NMEPs was attributed t o shunting of electrical current from JO5 spinous process stimulating needles through the metal rod to ground, thus preventing adequate stim ulation to the spinal cord. A modification of the transosseous techniq ue with epidural stimulation to improve test reliability is described.