MORPHOLOGY OF DYNAMIC GRACILOPLASTY COMPARED WITH THE ANAL-SPHINCTER

Dynamic graciloplasty for fecal incontinence includes gracilis muscle transposition around the anal canal as a new sphincter and subsequent electrical stimulation. The aim of electrical stimulation is to transf orm the gracilis fast-twitch, ''fatigue-prone' fibers into slow-twitch , ''fatigue-resistant' fibers to achieve a sustained tonic contraction . The latter is considered essential for sphincter function. Therefore , the following features of transposed gracilis muscle morphology were studied in nine patients before and after electrical stimulation: 1) the percentage of Type I fibers, 2) the lesser diameter of these fiber s, and 3) the positive collagen staining area. Furthermore, the extern al anal sphincter and gracilis muscle histology was investigated in si x autopsy cases. The mean percentage of Type 1, slow-twitch, fatigue-r esistant fibers in transposed gracilis muscle increased from 46 percen t before electrical stimulation to 64 percent (P < 0.01, paired Studen t's t-test) after electrical stimulation. The mean lesser diameter of these fibers did not change significantly (from 32 to 29 mum), and the mean percentage of collagen increased from 4 percent before electrica l stimulation to 7 percent (P < 0.01) afterward. The external sphincte r in cadavers demonstrated a predominance of Type I fibers (80 percent ) with a lesser diameter of 23 mum and a high percentage (12 percent) of collagen. Gracilis muscle histology was uniform at six different sa mple sites in these cadaver dissections. We conclude that electrical s timulation induces histologic changes in transposed gracilis muscle, a llowing this muscle to function as an external anal sphincter.