Afferent Fibers in the Ventral Root

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Abstract

The dorsal rhizotomy was one of the earliest operations used for the treatment of chronic, intractable, segmental pain. The theoretical basis underlying the use of this procedure was the law of separation of function of the spinal roots that implies, among other things, that sensory fibers are located in the dorsal root and motor fibers are located in the ventral roots. On this basis, it should be possible by cutting the appropriate dorsal roots to relieve pain for any particular part of the body at the cost of making that part of the body anesthetic. Unfortunately, however, the dorsal rhizotomy seems to have a relatively low success rate in that the pain is often not relieved or is relieved for a variable period of time and then returns. Many different reasons may account for these failures, but one reason that is not often considered is that the law of separation of function of the spinal roots may not be accurate. This is pertinent at the present time, because large numbers of ventral root afferent fibers have recently been discovered. This review summarizes the work, both old and new, on ventral root afferents with particular emphasis on possible clinical applications. In particular, it is pointed out that the ventral root afferent fibers are probably present in humans and, if so, they may be involved in explanations for the failure of dorsal rhizotomy to relieve chronic pain. If these fibers are important, then they can be removed by a dorsal root ganglionectomy, which would remove both the dorsal and ventral root afferent fibers, as opposed to a dorsal rhizotomy, which would remove only the dorsal root afferent fibers.

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