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This novel method for intraoperative monitoring of spinal motor conduction appears to meet all of the goals outlined above. Although the risk of postoperative motor deficit is relatively low for the majority of spine surgeries (for example, a simple disc), high-risk procedures, such as tumor resection, correction of vascular abnormalities, and correction of major deformities, should benefit from the virtually immediate and accurate knowledge of spinal motor conduction provided by this new monitoring approach.

SUMMARY1. Single-motor-unit activity was recorded from flexor carpi radialis of two human subjects.2. A large number of units showed repetitive doublets at the onset of slow recruitment. A unit starting with doublets would transfer to a normal firing pattern as the force increased.3. At different speeds of ramp contractions, the number of doublets discharging at the onset of contraction decreased as the speed of contraction increased.4. Both low-and high-threshold units discharged repetitive doublets. Motor units which could discharge doublets showed higher maximal firing rates than those units which did not fire doublets.5. Short interspike intervals were also observed at the onset ofballistic movements. From the comparison of these short interspike intervals and the short intradoublet intervals we suggest that the two arise from two distinct phenomena in the spinal cord.6. Linked potentials were observed both with single spikes and doublets. Their origin may lie in the spinal cord or the muscle unit itself or both.