The traditional bladder stimulator, the Finetech-Brindley Stimulator, and now the Vocare (NeuroControl Corp., Cleveland, Ohio) operates by stimulating the sacral anterior roots . This system has two primary drawbacks, which the Praxis system was designed to overcome: (1) posterior sacral rhizotomies are done, via a laminectomy, to achieve an areflexive bladder with increased capacity; (2) a sacral laminectomy is done to access the anterior sacral roots for fitting cuff-type electrodes. The rhizotomy procedure eliminates reflex erection in male recipients. Further, Creasey  states that "a patient who has the rhizotomies but does not use the implant (stimulator) would therefore be expected to become more constipated."
In August 1998, the Praxis FES-24A stimulator (Figure 17.1B) was developed by Neopraxis Pty. Ltd., and implanted in Subject B (35-year-old male paraplegic subject; ASIA: A, T10). Eighteen channels were used for stimulating individual nerves or branches for muscle contractions and limb movements, including exercise, pressure relief, standing, and stepping. The electrodes implanted for epineural stimulation were ten thin flexible platinum cuffs (Flexi-Cuff) that were sized, cut, and sutured closed with at least twice the diameter of encircled nerve. The other eight electrodes were 3-mm-diameter platinum buttons that were placed on the epineurium. Each button has an attached Dacron mesh surround that was sutured to the adjacent connective tissue on each side of the nerve.
Three channels for bilateral sacral root stimulation (S2-4) for bladder control (bowel control and erection, if possible) were provided. Sacral root stimulation was achieved by three pairs of LPR electrodes (10-mm long, solid platinum tubing of 1.0-mm diameter) inserted into the external sacral foramina in a lateral direction to follow and to stimulate the nerve roots epidurally. One further channel was connected to an epidural spinal cord stimulating electrode (Pisces Quad: Medtronic Inc., Minneapolis, Minnesota) for conus medullaris modulation of spastic bladder and bowel reflexes.
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