SELECTIVE DORSAL ROOT BLOCKADE USING SPINAL ENDOSCOPY AND ELECTRO-PHYSIOLOGY

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We aimed to develop a method of the selective dorsal root blockade under the endoscopic visual field. We achieved this goal by combining endoscopic observation with spinal cord potential mesurement. First, we developled a method of accurately identifying the dorsal roots for the corresponding afferent nerves. Then, we applied blockade on the roots under endoscopic view and evaluated the selectivity of the blockade.Methods : We used an endoscope with an external diameter of 1.8 mm, which consisted of the image-fiber, light-guide and a flush lumen. Goats were anesthetized and mechanically ventilated. After small laminectomy on lower thoracic vertebrae, we inserted this endoscope carefully into subarachnoid space and observed structures in the space. Then we inserted an eight polar catheter-type electrode into the visalized space to record evoked potentials. The distance between the pole of the catheter was 1 cm. The each pole could be distinguished by marks. Using endoscopy, we tried to … More determine the spatial relationship between these poles and dorsal roots. We chose the neighboring pairs of poles sequentially from the tip of catheter for bipolar recording. To stimulate peripheral nerves, we inserted needle-type electrodes into Th11 and Th12 intercostal nerves. We obtained sequential recordings of potentials from dorsal surface of the cord evoked by stimulating each intercostal nerve. By combining endoscopy with evoked potentials, we tried to identify the dorsal roots for the corresponding afferent nerve. Under endoscopic view, we applied a dose of 0.03 or 0.3 ml of 3% lidocaine solution on the dorsal root regarded as Th11. We obtained sequential recordings of evoked potentials after blockade and tried to determine the effects of blockade. At the end of each experiment, we dissected the animal and ensured the intercostal nerve originating from the root.Results : With the endoscope, we could determine the spatial relationship between the recording electrode and dorsal roots. Shapes of evoked potentials changed characteristically according to the relative position between roots and poles. Thus we could identify the dorsal root and the corresponding afferent nerve using the recording electrode as a cue. After the Th11 root blockade with 0.3 ml of 3% lidocaine solution, potentials evoked by Th11 and Th12 stimulation was both depressed. After a dose of 0.03 ml injection, potentials evoked by ipsilateral Th11 stimulation was depressed without change on potentials by contralateral Th11 and Th12 stimulationDiscussions and Conclusions : By combining endoscopy with the electro-physiological technique, we could identify the dorsal roots for the corresponding afferent nerves. We could also evaluate the selectivity of the blockade using this technique. This method can provide a useful tool for selective dorsal root blockade. Less