Introduction: Few studies describe in vivo stimulation mapping nerve root innervations in large numbers of individuals. This prospective study examines myotomal innervation via direct stimulation of nerve roots during spine surgery.

Methods: Patients undergoing surgical procedures includding: laminectomy, foraminotomy, ACDF, and discectomy were candidates for the study. EMG needle electrodes were placed in muscles that are generally accepted to be innervated by the roots under study. Additionally, recordings were also done from muscles that are commonly innervated by roots above and below the spinal levels undergoing decompression. Prior to testing a train-of-four was used to demonstrate that muscle relaxant had worn off. Three regions of the root were stimulated. The axilla and shoulder, which we define as the most inferior and superior point on the nerve respectively, and the midpoint region between the two. Stimulation parameters are as follows: 2.16 Hz, a pulse width of 200 microseconds, and a stimulation current of 0.1 to 2 mA. We also compared stimulation thresholds for pathologic roots and adjacent healthy roots, when there was adequate surgical exposure.

Results: A total of 2617 stimulation's were performed in 170 patients. Table I shows the distribution of threshold values per location on the root. Table II shows the percentage of muscle EMG activation for a given root, as a function of the total number of activations at that muscle. Data collection is ongoing.

Conclusions: The goal of this research was to investigate the myotomal innervations of cervical and lumbar nerve roots via in-vivo stimulation during surgeries for spinal decompression. In 15-20% of the roots stimulated we find activations outside of the standard innervations. These preliminary findings indicate that intraoperative testing of roots may be helpful in correlating specific patient symptoms with the actual pathological root when imaging studies are equivocal or unavailable.

Patient Care: Offer a statistical map of root to muscle innervations from the cervical and lumbosacral regions.

Learning Objectives: Gain a better understanding of the root to muscle innervation mapping

References: 1. Phillips, L, and Park, TS. (1991). “Electrophysiological Mapping of the Segmental Anatomy of the Muscles of the Lower Extremity”. Muscle and Nerve, 14:1213-1218 2. Thage O. (1965).“The Myotomes L2-S2 in Man”, Acta. Neurol. Scand. Suppl., 13(1):241-243. 3. Tsao BE, Levin KH, and Bodner RA. (2003). “Comparison of surgical and electrodiagnostic findings in single root lumbosacral radiculopathies”. Muscle and Nerve., 72:60-64. 4. Levin KH, Maggiano HJ, and Wilbourn AJ. (1996). “Cervical radiculopathies: Comparison of surgical and EMG localization of single-root lesions”. Neurology., 46:1022-1025. 5. Holland, N, Lukaczyk, T, Riley, L, and Kostuik, J. (1998). “Higher Electrical Stimulus Intensities Are Required to Activate Chronically Compressed Nerve Roots: Implications for Intraoperative Electromyographic Pedicle Screw Testing” Spine 23(2): 224-227