Differential effects of sacral anterior root stimulation on anal sphincter and colorectal motility in spinally injured man.

The motility responses of the sigmoid colon, rectum and external anal sphincter to sequential electrical stimulation of the anterior sacral roots (S2, S3 and S4) were studied in five patients with traumatic spinal cord injury. Identical and reproducible results were obtained. S2 stimulation provoked isolated low-pressure colorectal contractions. S3 stimulation initiated high-pressure colorectal motor activity which appeared peristaltic and was enhanced with repetitive stimuli. This response appeared to be frequency-dependent. S4 stimulation increased colonic and rectal tone. External sphincter activity was stimulated in increasing order from S2 to S4. These observations directly elucidate the central control of colorectal motility and may have implications in the treatment of severe constipation following spinal injury.