Analysis of chronic morphologic changes of small bowel in electrically stimulated canine island-flap rectus abdominis muscle stomal sphincters.
OBJECTIVE
Dynamic myoplasty to achieve fecal continence has been used in humans with varying results. A potential complication of the use of dynamic skeletal sphincters to attain fecal continence is the development of ischemic strictures within the bowel encircled by the functional sphincter. This study examines the histologic changes present in the bowel wall used to create a functional dynamic island-flap stomal sphincter in a chronic canine model.


METHODS
The rectus abdominis muscles of canines were used to create island-flap stomal sphincters. Eight dynamic island-flap stomal sphincters were created from the rectus abdominis muscles in mongrel dogs by wrapping them around a blind loop of distal ileum that was no longer in continuity with the terminal small bowel. Temporary pacing electrodes were secured intramuscularly near the intercostal nerve entry point and connected to a subcutaneously placed pulse stimulator. Two different training protocols resulting in different contractile properties were used: Program A (n = 4) and Program B (n = 4). The island-flap sphincters were trained over 3 months to generate stomal intraluminal pressures of more than 60 mmHg in all animals. The intact sphincters, normal bowel, and contralateral stomal bowel were obtained when the animals were killed. Specimens were processed with paraffin embedding, sectioned, and stained with trichrome and hematoxylin-and-eosin stains. Measurements of the different bowel layers were made with a micrometer. The muscular sphincters were biopsied before and after training. Fiber-type histochemistry was performed with a monoclonal antibody to the fast isoforms of myosin. Pretrained and posttrained skeletal muscle specimens were examined histologically.


RESULTS
The bowel wall within the functional dynamic stomal sphincter did not exhibit any significant architectural changes related to ischemic fibrosis or mucosal damage. A significant fiber-type conversion was achieved in both training groups with Programs A and B, with a >50 percent conversion from fatigue-prone (type II) muscle fibers to fatigue-resistant (type I) muscle fibers. Biopsy specimens revealed that fiber-type transformation was uniform throughout the sphincters. Skeletal muscle fibers within both groups demonstrated a reduction in their fiber diameter. There was no evidence of significant fibrosis or deposition of fat within the skeletal muscle of the sphincters.


CONCLUSIONS
Results of our experiment suggest that our anterior abdominal wall dynamic island-flap stomal sphincter, which generates a contractile force over the bowel wall capable of producing enough stomal pressure to achieve fecal continence, is not intrinsically harmful to the bowel that it encircles. The transformation of skeletal muscle to fatigue-resistant (type I) fibers occurred uniformly throughout the skeletal muscle sphincters without evidence of muscle fiber damage or significant fibrosis.
Majzoub
R K
RK
Division of Plastic and Reconstructive Surgery, Department of Surgery, University of Louisville, Louisville, Kentucky, USA.
Bardoel
J W
JW
Ackermann
D
D
Maldonado
C
C
Barker
J
J
Stadelmann
W K
WK
D000818:Animals; D004195:Disease Models, Animal; D004285:Dogs; D004558:Electric Stimulation; D004566:Electrodes; D005242:Fecal Incontinence / Q000473:pathology / Q000601:surgery* / Q000662:veterinary; D005355:Fibrosis; D007511:Ischemia / Q000473:pathology*; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000637:transplantation*; D012007:Rectum / Q000098:blood supply / Q000601:surgery; D013524:Surgical Flaps