Unmyelinated axons in human ventral roots, a possible explanation for the failure of dorsal rhizotomy to relieve pain.

Human ventral roots were examined in the light and electron microscopes. The noteworthy finding is that all roots contain large numbers of unmyelinated axons, and that they make up 27 per cent of the total population of ventral root axons. The function of these unmyelinated axons is not known, but for various reasons it is probable that a significant number are sensory. If so these axons might explain the failure of dorsal rhizotomy to relieve pain, and dorsal root gangionectomy, which would remove both dorsal and ventral root afferents, might be the procedure of choice for those patients where rhizotomy is contemplated.