Neurostimulation for bladder evacuation: is sacral root stimulation a substitute for microstimulation?

Abstract

Objective To determine by anatomical and functional studies whether stimulation of sacral rootlets might permit selective stimulation of autonomic fibres, thus avoiding the detrusor/sphincter dyssynergia characteristic of current techniques of neurostimulation for bladder evacuation. Materials and methods In 10 male mongrel dogs, the S2 root was isolated and its constituent rootlets followed from their origin in the spinal cord to the point of exit from the dura. The entire root and the individual rootlets were then stimulated, including intra‐ and extra‐dural stimulation and at proximal, mid and distal levels. Results Neuroanatomical and histological findings showed that the rootlets of ventral S2 maintain their identity throughout their intradural course; some carry predominantly autonomic fibres, some predominantly somatic and some a mixture of the two. Conclusion It appears surgically feasible to identify, isolate and sever the predominantly somatic rootlets intradurally, sparing the predominantly autonomic rootlets for inclusion in extradural electrode placement around the entire sacral root, thus eliminating sphincteric interference with detrusor contraction for voiding at low pressure.

Microsurgical Anatomy of Lumbosacral Nerve Rootlets for Highly Selective Rhizotomy in Chronic Spinal Cord Injury

“…This made it possible for microelectrode techniques to stimulate groups of neurons and axons innervating the bladder detrusor in the sacral spinal cord, without simultaneous excitement of the EUS. It is evident that none of the rootlets are completely pure in dogs, but there is a definite predominance of autonomic fibers in some and somatic fibers in others (Probst et al, 1997). The existence of fiber connections between rootlets or subbundles could also account for the impurity of the rootlets.…”

Neural prostheses

“…Various modifications of ventral root stimulation have been attempted in order to achieve a more normal voiding pattern. These include selective microrhizotomy of the somatic component of the ventral rootlets as they emerge from the spinal cord (Probst et al 1997) or by fatiguing the somatic component by high‐frequency, low‐amplitude electrical stimulation (Shaker et al 1998). A promising approach is anodic blocking of the large somatic nerve fibres in order to obtain selective activation of the small parasympathetic fibres innervating the bladder (Fang & Mortimer, 1991; Accornero, 1977; Grunewald et al 1998).…”

Efficacy of different spinal nerve roots for neuromodulation of micturition reflex in rats

“…The threshold at which an action potential is generated depends on the fiber type and size and the stimulation parameters [ 22 ]. According to some studies on microsurgical anatomy of the lumbosacral VRTs, the VRT consists of several rootlets with similar calibers [ 23 , 24 ]. Thus, because the stimulation parameters, fiber type, and caliber of the rootlets in the VRTs are consistent, we hypothesized that the number of rootlets involved may affect bladder contraction.…”