Dynamic rectus abdominis muscle flap for intestinal stomal continence: a systematic approach.

Several attempts to create a continent stomal sphincter using dynamic myoplasty with limited success have been reported. Denervation atrophy and early muscle fatigue have plagued all reported attempts to make a continent stoma a reality. To address this problem in a series of experiments, we designed a stomal sphincter using the most caudal segment of the rectus abdominis muscle. Then, we performed a study to determine whether a sphincter created with a rectus abdominis muscle island flap could maintain stomal continence in the short term. We found that when stimulated using two different electrical stimulation protocols, in all cases the rectus abdominis muscle sphincter generated peak pressures well above those needed to maintain stomal continence (60 mm Hg). All sphincters were able to maintain stomal continence at all intraluminal bowel pressures tested. We found one of these protocols to be far superior and reached 4 hours of stomal continence after 8 to 10 weeks of electrical stimulation.

Analysis of chronic morphologic changes of small bowel in electrically stimulated canine island-flap rectus abdominis muscle stomal sphincters.

PURPOSE: 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. CONCLUSION: 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.

Swine composite tissue allotransplant model for preclinical hand transplant studies.

Our laboratory previously developed and used an orthotopic radial forelimb osteomyocutaneous flap in the pig as a preclinical composite tissue allograft (CTA) model. To ensure that it mimicked the clinical situation as closely as possible we developed this model taking many immunologic and reconstructive considerations into account. While our original pig CTA model was ideal for studying the methods of preventing skin, muscle, bone, vessel and nerve rejection, and systemic toxicity, it did not include specialized tissues/structures of a joint and digit. Therefore, we were unable to evaluate rejection of these specialized tissues and their functional properties. Recognizing the importance of assessing joint rejection and function in hand transplantation research we developed a new swine forelimb CTA model that included the animal's medial digit. The present study describes the anatomy and the transplantation technique used in this new preclinical CTA model. We transplanted a radial osteomyocutaneous flap that included the medial digit between two size- (17-21 kg) and age- (6-8-week) matched farm pigs. We removed the digit from the recipient pig's forelimb in continuity with a section of the radial bone and replaced it with the same structure transplanted from a donor pig. After transplantation, a full-length cast was placed on the recipient pig's operated limb and changes in flap color, temperature and the presence of edema were monitored continuously for 6 h, and then regularly at predetermined intervals over 4 days. No weight bearing restrictions were placed on the animal's operated limb. After 4 days, the animal was euthanized. Direct visual monitoring of the allograft during 4 days revealed it was viable with no signs of graft failure due to technical complications associated with the transplant procedure. Upon waking from anesthesia, the animal stood and wandered freely about its cage with no apparent difficulty. Based on the animal's high level of activity at this time, we concluded that the procedure caused it minimal morbidity. At 4 days after the operation, early signs of rejection (skin erythema and edema) were observed. By incorporating a digit into our original CTA pig forelimb model we have made it a better model for performing preclinical hand transplant studies. The added advantage of being able to assess methods of preventing rejection in the specialized joint/digital tissues (articular cartilage, digital flexor and extensor systems, the nail complex) and assess long-term function of these structures is important. The fact that the procedure does not cause major morbidity to the animal makes it possible to conduct long-term graft survival and functional studies.