Radiofrequency neurolysis in a clinical model. Neuropathological correlation

Reports differ on which nerve fibers are affected by radiofrequency lesions made in peripheral nerves, some stating that primarily the myelinated delta and unmyelinated C fibers are destroyed, others stating that the destruction affects all sizes of nerve fibers and both myelinated and unmyelinated fibers. This study was designed to confirm one of those two findings, and to study the role that different temperatures might play in determining which fibers are affected. Radiofrequency lesions (85 degrees C for 2 minutes) were made in dogs by placing a temperature-monitored electrode into the lumber intervertebral foramina. The dogs were killed at intervals up to 6 weeks after rhizotomy, and the lesions were studied by light and electron microscopy. In all lesions, there was a total loss of unmyelinated fibers and a nearly total loss of myelinated fibers. In other dogs, 2-minute lesions were made at 45 degrees, 55 degrees, 65 degrees, and 75 degrees C, and the lesions examined 1 week later. Again, all sizes and all types of fibers were destroyed.