Motor evoked potential as a reliable method to verify the conductivity of anterior spinal roots in brachial plexus surgery: an experimental study on goats.

The goal of this experimental study was to confirm the reliability of motor evoked potential (MEP) in testing the function of anterior motor roots in brachial plexus surgery. On central stimulation, nerve compound action potentials (NCAPs) are registered from the exposed spinal nerves. If NCAPs can be recorded, the anterior root is considered to be intact. Two factors might cause positive recordings even in the presence of an avulsed anterior motor root: volume conduction, and impulse transmission through an intact posterior root. In five Nubian goats, spinal nerves C6, C7, and their corresponding spinal roots were dissected. On central stimulation, NCAPs were repeatedly recorded from the surface of all ten spinal nerves. Then, the anterior motor roots were transsected and central stimulation repeated. NCAPs disappeared irreversibly in all ten tested spinal nerves. The experiment showed that, on central stimulation, NCAPs cannot be recorded from spinal nerves unless the anterior root is intact.