Dynamic Myoplasty Research Articles

Electrically Stimulated Rectus Abdominis Muscle Flap to Achieve Enterostomal Continence: Development of a Functional Canine Model

Dynamic myoplasty has many clinical applications and has proven to be a versatile surgical procedure with great promise. This procedure has been used to achieve fecal/urinary continence, as in the dynamic graciloplasty, and to augment cardiac ventricular function, as is commonly seen with dynamic latissimus cardiomyoplasty. In the present study, the authors describe a functional innovative island flap sphincter created from the rectus abdominis muscle in a large-animal model to provide stomal continence for future clinical studies. The caudal region of the rectus abdominis muscle in eight mongrel canines (23 to 25 kg) was investigated through anatomical dissections during which the location of the neurovascular pedicles and the intersegmental muscle dimensions between the muscle inscriptions were noted. The rectus abdominis muscle was used to create functional dynamic stomal sphincters that were trained with subcutaneously implanted pulse stimulators. The neurovascular pedicles were consistently found in similar locations along the posterior medial aspect of the caudal portion of the canine's rectus abdominis muscle. The vertical height of the deep inferior epigastric pedicle and caudal intercostal nerve muscular mean entry points were 6.75 +/- 1.89 cm and 7.44 +/- 0.86 cm, respectively. The mean caudal intersegmental muscle length of the rectus abdominis muscle used to create the sphincter was 9.69 +/- 1.81 cm. The canine rectus abdominis muscle has reliable anatomical locations where the neurovascular pedicle may be found. This canine muscle may be used to create a continent island flap stomal sphincter. This large-animal sphincter model is versatile, durable, and easy to manipulate, with minimal morbidity to the animal.

Experimental model of continent colostomy using rectus abdominis neosphincteroplasty.

Use of dynamic myoplasty to create a continent stoma has produced promising results, but long-term stoma continence has not been achieved. The aim of the study was to establish and test a new model. Three types of dynamic rectus abdominis sphincteroplasty around a colostomy and two conditioning protocols were tested in ten domestic pigs. Continence was assessed by means of conventional defaecography and neosphincter manometry after 8 and 12 weeks. The neosphincter muscle was studied histologically to assess the transformation of muscle type. Use of a distal rectus muscle sling surrounding the stoma by 270 degrees with a low-frequency conditioning protocol achieved a continent colostomy for more than 12 h on each of 5 consecutive days. The neosphincter had a 40-mm high-pressure segment with mean pressure of 74 (range 67-82) mmHg. The proportion of type I muscle fibres increased from 38 (range 32-42) to 74 (range 66-78) per cent after 12 weeks of conditioning. This pilot study demonstrated the feasibility of a continent stoma in an animal model with a dynamic rectus neosphincter. Long-term results should be confirmed in a larger series before use in humans can be considered.

Dynamic graciloplasty for urinary incontinence: the potential for sequential closed-loop stimulation

Muscle tissue transplantation applied to regain or dynamically assist contractile functions is known as ‘dynamic myoplasty’. Success rates of clinical applications are unpredictable, because of lack of endurance, ischemic lesions, abundant scar formation and inadequate performance of tasks due to lack of refined control. Electrical stimulation is used to control dynamic myoplasties and should be improved to reduce some of these drawbacks. Sequential segmental neuromuscular stimulation improves the endurance and closed-loop control offers refinement in rate of contraction of the muscle, while function-controlling stimulator algorithms present the possibility of performing more complex tasks. An acute feasibility study was performed in anaesthetised dogs combining these techniques. Electrically stimulated gracilis-based neo-sphincters were compared to native sphincters with regard to their ability to maintain continence. Measurements were made during fast bladder pressure changes, static high bladder pressure and slow filling of the bladder, mimicking among others posture changes, lifting heavy objects and diuresis. In general, neo-sphincter and native sphincter performance showed no significant difference during these measurements. However, during high bladder pressures reaching 40 cm H 2O the neo-sphincters maintained positive pressure gradients, whereas most native sphincters relaxed. During slow filling of the bladder the neo-sphincters maintained a controlled positive pressure gradient for a prolonged time without any form of training. Furthermore, the accuracy of these maintained pressure gradients proved to be within the limits set up by the native sphincters. Refinements using more complicated self-learning function-controlling algorithms proved to be effective also and are briefly discussed. In conclusion, a combination of sequential stimulation, closed-loop control and function-controlling algorithms proved feasible in this dynamic graciloplasty-model. Neo-sphincters were created, which would probably provide an acceptable performance, when the stimulation system could be implanted and further tested. Sizing this technique down to implantable proportions seems to be justified and will enable exploration of the possible benefits.

Linear pressure profiles and symmetric findings in the stimulated gracilis muscle.

This is the first report of linear pressure profiles and symmetric findings in preoperative and postoperative (after gracilis muscle retraining) patients. Length of the anal canal and symmetry have been well documented in the literature as significant parameters in the maintenance of anal incontinence. Significant improvement of these parameters should play a critical role in the functional outcome of the stimulated gracilis. Six patients underwent preoperative and postoperative anorectal manometry using an eight-channel radial catheter. Pressures were collected at 8 Hz using an automated continuous pullout technique (1 mm/sec). Preoperative and posttraining resting and squeeze pressures, pressure volumes, anal canal length, and linear and cross-sectional images were compared. Resting pressures significantly improved from 13.7 mmHg to 26.8 mmHg (P < 0.02). The squeeze pressure significantly improved from 28.67 mmHg to 62.9 mmHg (P < 0.02). The pressure volume increased from 10,429 mmHg to 26,162 mmHg. Anal canal length increased from an abnormal length of 2.95 cm to normal length of 3.55 cm (P < 0.04). The percentage of sphincter asymmetry decreased from 28.6 percent to 23.5 percent (P < 0.01). The most striking observation was the impact the gracilis muscle had on correcting the geographic cross sections as it wrapped more than 360 degrees from the proximal to distal anal canal. Patients were significantly improved, with four of the six patients completely continent to solid stool. Two of the six patients had minor episodes of seepage. Preoperatively, all patients were grossly incontinent to solid stool. Significant improvement in resting pressure, pressure volume, anal canal length, and cross-sectional symmetry has led to a significant improvement in anal incontinence after dynamic myoplasty.

Preconditioning of latissimus dorsi muscle flaps with monophosphoryl lipid a.

The use of dynamic myoplasty to restore function to failing organs is an exciting new application of skeletal muscle flaps. A complication of large flap elevation that can compromise flap function is ischemia-induced necrosis; one approach to minimizing this is to pretreat tissues with ischemic preconditioning. The purpose of this study was to determine whether systemic administration of monophosphoryl lipid A, a drug known to mimic late-phase ischemic preconditioning in the heart, could reduce ischemia-induced necrosis in latissimus dorsi muscle flaps. Forty latissimus dorsi muscle flaps from 20 Sprague-Dawley rats were allocated into four groups. In group I (n = 10), flaps were not preconditioned and served as controls. In group II (n = 10), flaps received ischemic preconditioning with two 30-minute periods of ischemia interspersed by 10 minutes of reperfusion. In group III (n = 10), rats received an intravenous bolus of approximately 0.3 ml of monophosphoryl lipid A vehicle only. In group IV (n = 10), rats received an intravenous bolus of 450 microg/kg of monophosphoryl lipid A and vehicle. Twenty-four hours after treatment, all latissimus dorsi muscle flaps were elevated on a single neurovascular pedicle and subjected to 4 hours of ischemia. After 72 hours of reperfusion, latissimus dorsi muscles were harvested, weighed, stained with nitroblue tetrazolium, and assessed for percent necrosis using digitized images of muscle sections and computerized planimetry. The percent necrosis in ischemic preconditioning-treated flaps (group II) was significantly reduced by 57 percent (p < 0.05) compared with control flaps (group I). The percent necrosis in flaps treated with monophosphoryl lipid A (group IV) was significantly reduced by 58 percent (p < 0.05) compared with vehicle-control flaps (group III). There was no difference in mean percent necrosis between ischemic preconditioning (group II) and monophosphoryl lipid A-treated (group IV) flaps or between ischemic preconditioning-control (group I) and monophosphoryl lipid A vehicle-control (group III) flaps. Intravenous administration of systemic monophosphoryl lipid A mimics the late-phase protective effect of ischemic preconditioning in the authors' rat latissimus dorsi muscle flap model.

A Technique for Sequential Segmental Neuromuscular Stimulation with Closed Loop Feedback Control

In dynamic myoplasty, dysfunctional muscle is assisted or replaced with skeletal muscle from a donor site. Electrical stimulation is commonly used to train and animate the skeletal muscle to perform its new task. Due to simultaneous tetanic contractions of the entire myoplasty, muscles are deprived of perfusion and fatigue rapidly, causing long-term problems such as excessive scarring and muscle ischemia. Sequential stimulation contracts part of the muscle while other parts rest, thus significantly improving blood perfusion. However, the muscle still fatigues. In this article, we report a test of the feasibility of using closed-loop control to economize the contractions of the sequentially stimulated myoplasty. A simple stimulation algorithm was developed and tested on a sequentially stimulated neo-sphincter designed from a canine gracilis muscle. Pressure generated in the lumen of the myoplasty neo-sphincter was used as feedback to regulate the stimulation signal via three control parameters, thereby optimizing the performance of the myoplasty. Additionally, we investigated and compared the efficiency of amplitude and frequency modulation techniques. Closed-loop feedback enabled us to maintain target pressures within 10% deviation using amplitude modulation and optimized control parameters (correction frequency = 4 Hz, correction threshold = 4%, and transition time = 0.3 s). The large-scale stimulation/feedback setup was unfit for chronic experimentation, but can be used as a blueprint for a small-scale version to unveil the theoretical benefits of closed-loop control in chronic experimentation.

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

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. 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. 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. 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.

Dynamic rectus abdominis muscle sphincter for stoma continence: an acute functional study in a dog model.

Fecal stomal incontinence is a problem that continues to defy surgical treatment. Previous attempts to create continent stomas using dynamic myoplasty have had limited success due to denervation atrophy of the muscle flap used in the creation of the sphincter and because of muscle fatigue resulting from continuous electrical stimulation. To address the problem of denervation atrophy, a stomal sphincter was designed using the most caudal segment of the rectus abdominis muscle, preserving its intercostal innervation as well as its vascular supply. The purpose of the present study was to determine whether this rectus abdominis muscle island flap sphincter design could maintain stomal continence acutely. In this experiment, six dogs were used to create eight rectus abdominis island flap stoma sphincters around a segment of distal ileum. Initially, the intraluminal stomal pressures generated by the sphincter using different stimulation frequencies were determined. The ability of this stomal sphincter to generate continence at different intraluminal bowel pressures was then assessed. In all cases, the rectus abdominis muscle sphincter generated peak pressures well above those needed to maintain stomal continence (60 mmHg). In addition, each sphincter was able to maintain stomal continence at all intraluminal bowel pressures tested.

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.

Re-animation of muscle flaps for improved function in dynamic myoplasty.

The authors report on a series of experiments designed to produce a skeletal muscle contraction functional for dynamic myoplasties. Conventional stimulation techniques recruit all or most of the muscle fibers simultaneously and with maximal strength. This approach has limitations in free dynamic muscle flap transfers that require the muscle to contract immediately after transfer and before re-innervation. Sequential stimulation of segments of the transferred muscle provides a means of producing non-fatiguing contractions of the muscle in the presence or absence of innervation. The muscles studied were the canine gracilis, and all experiments were acute studies in anesthetized animals. Comparison of conventional and sequential segmental neuromuscular stimulation revealed an increase in muscle fatigue resistance and muscle blood flow with the new approach. This approach offers the opportunity for development of physiologically animated tissue and broadening the abilities of reconstructive surgeons in the repair of functional defects.

Use of the rectus abdominis muscle for abdominal stoma sphincter construction: an anatomical feasibility study.

Permanent fecal abdominal stomas significantly decrease quality of life. Previous attempts to create continent stomas by using dynamic myoplasty procedures have resulted in disappointing outcomes, primarily owing to denervation atrophy of the muscle flap that was used in the creation of the sphincter and because of muscle fatigue resulting from continuous electrical stimulation that is received by the flap to force contraction. On the basis of these problems, we designed two separate studies: an anatomical study addressing flap denervation and a functional study addressing muscle fatigue. The present study addresses the first topic and was designed to develop a rectus abdominis muscle flap into a sphincter that was anatomically situated to create a stoma while preserving as much innervation as possible. In 24 rectus abdominis muscles of human cadavers, the neurovascular anatomy was defined, then the anatomical feasibility of two different muscle flap configurations was considered. The flaps investigated were the peninsula flap and island flap designs, with both using the most caudal segment of the rectus abdominis muscle in construction of the sphincter. Neither flap design required the killing of a nerve for stoma sphincter creation, resulting in minimal muscle denervation. The conclusion of our comparison was that the above, in conjunction with other features of the island flap design, such as muscle overlap after sphincter formation and abdominal wall positioning of the sphincter, made the island flap design better suited to stoma sphincter construction.

Three parameters optimizing closed-loop control in sequential segmental neuromuscular stimulation.

In conventional dynamic myoplasties, the force generation is poorly controlled. This causes unnecessary fatigue of the transposed/transplanted electrically stimulated muscles and causes damage to the involved tissues. We introduced sequential segmental neuromuscular stimulation (SSNS) to reduce muscle fatigue by allowing part of the muscle to rest periodically while the other parts work. Despite this improvement, we hypothesize that fatigue could be further reduced in some applications of dynamic myoplasty if the muscles were made to contract according to need. The first necessary step is to gain appropriate control over the contractile activity of the dynamic myoplasty. Therefore, closed-loop control was tested on a sequentially stimulated neosphincter to strive for the best possible control over the amount of generated pressure. A selection of parameters was validated for optimizing control. We concluded that the frequency of corrections, the threshold for corrections, and the transition time are meaningful parameters in the controlling algorithm of the closed-loop control in a sequentially stimulated myoplasty.

Refractory heart failure.

Managing patients with heart failure is rooted in appropriate recognition of the syndrome and subsequent tailoring of therapies to individual patients based on the stage of the disease. An individual with asymptomatic left ventricular dysfunction (the earliest stage of heart failure) is treated quite differently than a patient with more advanced heart failure manifested by problematic fluid retention, peripheral organ hypoperfusion with dysfunction, and several comorbidities. The latter patient requires aggressive pharmacologic intervention coupled with other creative strategies that are individually tailored to each individual"s unique clinical circumstance. The therapies available include long-term administration of parenteral inotropic therapy, dialysis, insertion of a ventricular assist device, cardiac transplantation, dynamic skeletal myoplasty, volume reduction surgery, or more standard (but higher risk) operative procedures. New drugs are constantly undergoing evaluation and may lead to additional therapeutic improvements in patients with advanced heart failure. The key is recognizing the appropriate place for more radical therapies.

Vascular delay in skeletal muscle: a model for microcirculatory studies.

Dynamic myoplasty is a relatively new use for muscle flaps and has led us to revisit the mechanisms of vascular delay as a means of optimizing blood supply to muscle flaps. Despite the well-documented effectiveness of vascular delay in skin flaps, vascular delay in muscle flaps has not been widely reported. Regardless of the many mechanisms postulated in the literature as contributors to the delay effect in skin, the one element common to all these hypotheses is the importance placed on changes in the microcirculation. Based on this factor, in the present study we developed and validated an animal model in which delay-induced microvascular changes could be measured in skeletal muscle flaps. We used the hairless mouse latissimus dorsi muscle flap because its vascular distribution is similar to that of humans and its thin structure will enable us in future studies to directly view and measure its microvasculature using videomicroscopy. In 12 animals, we found that delay significantly (p < 0.01) reduced necrosis of the distal part of the muscle from 57 +/- 9 percent in nondelayed flaps (n = 7) to 22 +/- 3 percent in delayed (n = 5) flaps. In these studies, we also determined that the hairless mouse latissimus dorsi muscle flap will serve as an excellent model for defining microvascular changes throughout delay.

The intramuscular arterial anatomy of the long head of biceps femoris muscle.

We have previously shown that the neurovascular anatomy and length of the long head of biceps femoris (LHBF) is suitable for its possible use in the creation of a dynamic perianal myoplasty to restore faecal continence. If intramuscular arterioarterial anastomoses exist between a muscle's vascular pedicles then the delay procedure, i.e. ligating the vascular pedicles to the transposed section of the muscle, 4-6 wk before transposition, can be used to improve blood flow to the distal part of the transposed muscle. The intramuscular arterial anatomy of 20 biceps femoris muscles was shown by dissection (14) or radiographically (6). The mean entry point of the upper major vascular pedicle to the LHBF was 12 cm (S.D. 3.3) and the mean length of the LHBF was 36.8 cm (S.D. 1.8). Therefore the ratio between upper major vascular pedicle entry point and muscle length in 95% of specimens was 0.33 (0.2). In the present study intramuscular arterioarterial anastomoses were found between the arterial pedicles to the nontransposed and transposed sections of the LHBF and between the long and short heads of this muscle. Using the delay procedure would therefore theoretically allow the intramuscular arterioarterial anastomoses between the arterial pedicle to the nontransposed and transposed sections of the LHBF to open up enhancing blood flow to the distal part of the myoplasty.

Dynamic myoplasty in growing dogs as a feasibility study for treatment of fecal incontinence

The feasibility of skeletal muscle transposition and electrical stimulation (dynamic myoplasty) for treatment of fecal incontinence has been shown in adults. It might be attractive to use such a technique in pediatric patients. Therefore, the influence of growth on skeletal muscle transposition and stimulation was studied in five puppies. In each dog, two neosphincters were constructed around a Thiry-Vella loop by using a dissected sartorius muscle with the neurovascular supply intact. In each of these five puppies, one of these muscles was electrically stimulated during a mean of 19 weeks (one puppy died during the first postoperative week). Muscle biopsies showed an increase in the percentage type I, fatigue-resistant muscle fibers from 61 to 94 in electrically stimulated sartorius neosphincters, but also an increase from 57 to 67 percent in transposed nonstimulated sartorius muscles. The diameter of these type I fibers during growth increased 36% in electrically stimulated sartorius neosphincters and 55% in nonstimulated sphincters. Function of the neosphincters was tested with the inflow of saline in the Thiry-Vella loop. It was shown that the stimulated neosphincters were capable of inhibiting flow (which corresponded to manometric pressure registrations), but the nonstimulated sphincters were unable to inhibit flow. The experiments were complicated by infection and necrosis around the implanted stimulators in four puppies (which required reimplantation). We conclude that a dynamic myoplasty for fecal incontinence is feasible in growing puppies but that the technique is unacceptable during rapid growth because of the risks of infection and dislocation of the implanted device.