Treatment of Tourniquet-Induced Ischemia Reperfusion Injury with Muscle Progenitor Cells

Effect of valproic acid upon skeletal muscle subjected to prolonged tourniquet application

Background

Valproic acid (VPA), a histone deacetylase inhibitor, has shown improved outcomes when used as a pharmaceutical intervention in animal studies of hemorrhage, septic shock, and combined injuries. This study was designed to investigate the ability of VPA to mitigate ischemia-reperfusion injury produced by prolonged tourniquet application to an extremity.

Methods

The ischemia-reperfusion model in anesthetized rats was established using hemorrhage and a 3-hour tourniquet application. VPA was administered intravenously prior to tourniquet wear and removal. Ischemia-reperfusion injury was evaluated by investigating pathway signaling, immune modulation of cytokine release, remote organ injury, and skeletal muscle function during convalescence.

Results

We found that VPA sustained Protein kinase B (Akt) phosphorylation and Insulin-like growth factor signaling and modulated the systemic release of interleukin (IL)-1β, tumor necrosis factor alpha, and IL-6 after 2 hours of limb reperfusion. Additionally, VPA attenuated a loss in glomerular filtration rate at 3 days after injury. Histological and functional evaluation of extremity skeletal muscle at 3, 7, and 21 days after injury, however, demonstrated no significant differences in myocytic degeneration, necrotic formation, and maximal isometric tetanic torque.

Conclusions

Our results demonstrate that VPA sustains early prosurvival cell signaling, reduces the inflammatory response, and improves renal function in a hemorrhage with prolonged ischemia and reperfusion model. However, these do not translate into meaningful preservation in limb function when applied as a pharmaceutical augmentation to tourniquet wear.

Level of evidence

IV.

Efficacy of non-surgical interventions for promoting improved functional outcomes following acute compartment syndrome: A systematic review

BACKGROUND

Acute compartment syndrome (ACS) is a devastating complication which develops following a traumatic extremity injury that results in increased pressure within osteofascial compartments, thereby leading to ischemia, muscle and nerve necrosis, and creates a life-threatening condition if left untreated. Fasciotomy is the only available standard surgical intervention for ACS. Following fasciotomy the affected extremity is plagued by prolonged impairments in function. As such, an unmet clinical need exists for adjunct, non-surgical therapies which can facilitate accelerated functional recovery following ACS. Thus, the purpose of this systematic review was to examine the state of the literature for non-surgical interventions that aim to improve muscle contractile functional recovery of the affected limb following ACS.

METHODS

English language manuscripts which evaluated non-surgical interventions for ACS, namely those which evaluated the function of the affected extremity, were identified as per PRISMA protocols via searches within three databases from inception to February 2022. Qualitative narrative data synthesis was performed including: study characteristics, type of interventions, quality, and outcomes. Risk of bias (RoB) was assessed using the Systematic Review Centre for Laboratory Animal Experimentation's (SYRCLE) RoB tool and reported level of evidence for each article.

RESULTS

Upon review of all initially identified reports, 29 studies were found to be eligible and included. 23 distinct non-surgical interventions were found to facilitate improved muscle contractile function following ACS. Out of 29 studies, 15 studies which evaluated chemical and biological interventions, showed large effect sizes for muscle function improvement.

CONCLUSIONS

This systematic review demonstrated that the majority of identified non-surgical interventions facilitated an improvement in muscle contractile function following pathological conditions of ACS.

Administration of particulate oxygen generators improves skeletal muscle contractile function after ischemia-reperfusion injury in the rat hindlimb

Extended tourniquet application, often associated with battlefield extremity trauma, can lead to severe ischemia-reperfusion (I/R) injury in skeletal muscle. Particulate oxygen generators (POGs) can be directly injected into tissue to supply oxygen to attenuate the effects of I/R injury in muscle. The goal of this study was to investigate the efficacy of a sodium percarbonate (SPO)-based POG formulation in reducing ischemic damage in a rat hindlimb during tourniquet application. Male Lewis rats were anesthetized and underwent tourniquet application for 3 h at a pressure of 300 mmHg. Shortly after tourniquet inflation, animals received intramuscular injections of either 0.2 mg/mL SPO with catalase (n = 6) or 2.0 mg/mL SPO with catalase (n = 6) directly into the tibialis anterior (TA) muscle. An additional Tourniquet-Only group (n = 12) received no intervention. Functional recovery was monitored by in vivo contractile testing of the hindlimb at 1, 2, and 4 wk after injury. By the 4 wk time point, the Low-Dose POG group continued to show improved functional recovery (85% of baseline) compared with the Tourniquet-Only (48%) and High-Dose POG (56%) groups. In short, the low-dose POG formulation appeared, at least in part, to mitigate the impact of ischemic tissue injury, thus improving contractile function after tourniquet application. Functional improvement correlated with maintenance of larger muscle fiber cross-sectional area and the presence of fewer fibers containing centrally located nuclei. As such, POGs represent a potentially attractive therapeutic solution for addressing I/R injuries associated with extremity trauma.NEW & NOTEWORTHY Skeletal muscle contraction was evaluated in the same animals at multiple time points up to 4 wk after injury, following administration of particulate oxygen generators (POGs) in a clinically relevant rat hindlimb model of tourniquet-induced ischemia. The observed POG-mediated improvement of muscle function over time confirms and extends previous studies to further document the potential clinical applications of POGs. Of particular significance in austere environments, this technology can be applied in the absence of an intact circulation.

Effects of Trans-Cinnamaldehyde on Reperfused Ischemic Skeletal Muscle and the Relationship to Laminin

PURPOSE

Ischemia-reperfusion (I-R) injury is a serious problem caused by vascular trauma, tourniquet use and/or compartment syndrome. Studies have reported that skeletal muscle function is impaired due to the lower extremity I-R injury. There are insufficient studies on the treatment methods used for the recovery of dysfunction. This study is designed to investigate the effects of trans-cinnamaldehyde (TCA), a volatile oil of cinnamon structure, on the contractile dysfunction due to I-R injury of rat extensor-digitorum-longus (EDL) muscle.

MATERIALS AND METHODS

Sprague-Dawley rats were randomly divided into three groups. Except for the animals in the control group, all animals received saline (3-ml/kg) or TCA solution (30-mg/kg) which was administered orally three times with an 8-h interval before ischemia. After 24-hours, experimental groups were subjected to 3-h of lower extremity ischemia followed by 5-h reperfusion period. Then, the compound muscle action potential (CMAP) and mechanical activity of muscle were recorded using the standard electro-biophysical techniques.

RESULTS

There was a decrease in the maximum contractile force in I-R group compared to the control group (p < 0.05). Oxidative damage indicator (MDA) and antioxidant indicator (CAT) increased in the EDL muscle and serum samples in the I-R group (p < 0.05). Laminin expression showed a reduction in the I-R group (p < 0.05). It was seen that TCA achieve again the maximum contraction force in the EDL muscle (p < 0.05) and maintain the expression of laminin (p > 0.05).

CONCLUSION

We concluded that TCA has a potential protective effect with antioxidant effects against I-R injury and may maintain laminin levels.

In Silico and In Vivo Studies Detect Functional Repair Mechanisms in a Volumetric Muscle Loss Injury

IMPACT STATEMENT

Despite medical advances, volumetric muscle loss (VML) injuries to craniofacial muscles represent an unmet clinical need. We report an implantable tissue-engineered construct that leads to substantial tissue regeneration and functional recovery in a preclinical model of VML injury that is dimensionally relevant to unilateral cleft lip repair, and a series of corresponding computational models that provide biomechanical insight into mechanism(s) responsible for the VML-induced functional deficits and recovery following tissue-engineered muscle repair implantation. This unique combined approach represents a critical first step toward establishing a crucial biomechanical basis for the development of efficacious regenerative technologies, considering the spectrum of VML injuries.

Mechanisms by which hydrogen sulfide attenuates muscle function following ischemia-reperfusion injury: effects on Akt signaling, mitochondrial function, and apoptosis

Ischemia–reperfusion injury is caused by a period of ischemia followed by massive blood flow into a tissue that had experienced restricted blood flow. The severity of the injury is dependent on the time the tissue was restricted from blood flow, becoming more severe after longer ischemia times. This can lead to many complications such as tissue necrosis, cellular apoptosis, inflammation, metabolic and mitochondrial dysfunction, and even organ failure. One of the emerging therapies to combat ischemic reperfusion injury complications is hydrogen sulfide, which is a gasotransmitter that diffuses across cell membranes to exert effects on various signaling pathways regulating cell survival such as Akt, mitochondrial activity, and apoptosis. Although commonly thought of as a toxic gas, low concentrations of hydrogen sulfide have been shown to be beneficial in promoting tissue survival post-ischemia, and modulate a wide variety of cellular responses. This review will detail the mechanisms of hydrogen sulfide in affecting the Akt signaling pathway, mitochondrial function, and apoptosis, particularly in regards to ischemic reperfusion injury in muscle tissue. It will conclude with potential clinical applications of hydrogen sulfide, combinations with other therapies, and perspectives for future studies.

Effect of iloprost on contractile impairment and mitochondrial degeneration in ischemia-reperfusion of skeletal muscle

Purpose Acute lower extremity ischemia is still a main cause of mortality and morbidity in orthopedic traumatology and reconstructive surgery. In acute lower extremity ischemia, the skeletal muscles are the tissues that are the most vulnerable to ischemia. The aim of this study was to evaluate the effects of iloprost (IL) therapy on skeletal muscle contractile impairment and mitochondrial degeneration in an acute lower extremity ischemia-reperfusion rat model. Main Methods Forty Wistar albino rats were randomly divided into a control group and four experimental groups. Experimental groups were either subjected to 2 h of lower extremity ischemia followed by a 4-h reperfusion period or to 4 h of ischemia followed by an 8-h reperfusion period. Except for the animals in the control group, all animals received IL (1 ng/kg/min) or saline (1 ml/kg) by intraperitoneal infusion for 10 min immediately before reperfusion. At the end of the recording of skeletal muscle electrical activity and contractility, all rats were sacrificed by decapitation and muscle samples of lower extremity were immediately harvested for histopathologic analyses. Results After ischemia-reperfusion, a breakdown in the force-frequency curves of extensor digitorum longus muscle was observed, showing the diminished muscle contractility. However, IL significantly improved muscle contractility following injury induced by 2 h of ischemia followed by a 4-h reperfusion period. In addition, IL partially ameliorated mitochondrial degeneration in the muscle cells of ischemia groups. Conclusion This study indicates that immediate IL therapy repairs muscle damage especially after 2 h of ischemia and 4 h of reperfusion and therefore that IL improves contractile function.

Controlled delivery of SDF-1α and IGF-1: CXCR4(+) cell recruitment and functional skeletal muscle recovery

Therapeutic delivery of regeneration-promoting biological factors directly to the site of injury has demonstrated its efficacy in various injury models. Several reports describe improved tissue regeneration following local injection of tissue specific growth factors, cytokines and chemokines. Evidence exists that combined cytokine/growth factor treatment is superior for optimizing tissue repair by targeting different aspects of the regeneration response. The purpose of this study was to evaluate the therapeutic potential of the controlled delivery of stromal cell-derived factor-1alpha (SDF-1α) alone or in combination with insulin-like growth factor-I (SDF-1α/IGF-I) for the treatment of tourniquet-induced ischemia/reperfusion injury (TK-I/R) of skeletal muscle. We hypothesized that SDF-1α will promote sustained stem cell recruitment to the site of muscle injury, while IGF-I will induce progenitor cell differentiation to effectively restore muscle contractile function after TK-I/R injury while concurrently reducing apoptosis. Utilizing a novel poly-ethylene glycol PEGylated fibrin gel matrix (PEG-Fib), we incorporated SDF-1α alone (PEG-Fib/SDF-1α) or in combination with IGF-I (PEG-Fib/SDF-1α/IGF-I) for controlled release at the site of acute muscle injury. Despite enhanced cell recruitment and revascularization of the regenerating muscle after SDF-1α treatment, functional analysis showed no benefit from PEG-Fib/SDF-1α therapy, while dual delivery of PEG-Fib/SDF-1α/IGF-I resulted in IGF-I-mediated improvement of maximal force recovery and SDF-1α-driven in vivo neovasculogenesis. Histological data supported functional data, as well as highlighted the important differences in the regeneration process among treatment groups. This study provides evidence that while revascularization may be necessary for maximizing muscle force recovery, without modulation of other effects of inflammation it is insufficient.

The Development of Macrophage-Mediated Cell Therapy to Improve Skeletal Muscle Function after Injury

Skeletal muscle regeneration following acute injury is a multi-step process involving complex changes in tissue microenvironment. Macrophages (MPs) are one of the key cell types involved in orchestration and modulation of the repair process. Multiple studies highlight the essential role of MPs in the control of the myogenic program and inflammatory response during skeletal muscle regeneration. A variety of MP phenotypes have been identified and characterized in vitro as well as in vivo. As such, MPs hold great promise for cell-based therapies in the field of regenerative medicine. In this study we used bone-marrow derived in vitro LPS/IFN-y-induced M1 MPs to enhance functional muscle recovery after tourniquet-induced ischemia/reperfusion injury (TK-I/R). We detected a 15% improvement in specific tension and force normalized to mass after M1 (LPS/IFN-γ) MP transplantation 24 hours post-reperfusion. Interestingly, we found that M0 bone marrow-derived unpolarized MPs significantly impaired muscle function highlighting the complexity of temporally coordinated skeletal muscle regenerative program. Furthermore, we show that delivery of M1 (LPS/IFN-γ) MPs early in regeneration accelerates myofiber repair, decreases fibrotic tissue deposition and increases whole muscle IGF-I expression.

Can Cytoprotective Cobalt Protoporphyrin Protect Skeletal Muscle and Muscle-derived Stem Cells From Ischemic Injury?

BACKGROUND

Extremity trauma is the most common injury seen in combat hospitals as well as in civilian trauma centers. Major skeletal muscle injuries that are complicated by ischemia often result in substantial muscle loss, residual disability, or even amputation, yet few treatment options are available. A therapy that would increase skeletal muscle tolerance to hypoxic damage could reduce acute myocyte loss and enhance preservation of muscle mass in these situations.

QUESTIONS/PURPOSES

In these experiments, we investigated (1) whether cobalt protoporphyrin (CoPP), a pharmacologic inducer of cytoprotective heme oxygenase-1 (HO-1), would upregulate HO-1 expression and activity in skeletal muscle, tested in muscle-derived stem cells (MDSCs); and (2) whether CoPP exposure would protect MDSCs from cell death during in vitro hypoxia/reoxygenation. Then, using an in vivo mouse model of hindlimb ischemia/reperfusion injury, we examined (3) whether CoPP pharmacotherapy would reduce skeletal muscle damage when delivered after injury; and (4) whether it would alter the host inflammatory response to injury.

METHODS

MDSCs were exposed in vitro to a single dose of 25 μΜ CoPP and harvested over 24 to 96 hours, assessing HO-1 protein expression by Western blot densitometry and HO-1 enzyme activity by cGMP levels. To generate hypoxia/reoxygenation stress, MDSCs were treated in vitro with phosphate-buffered saline (vehicle), CoPP, or CoPP plus an HO-1 inhibitor, tin protoporphyrin (SnPP), and then subjected to 5 hours of hypoxia (< 0.5% O2) followed by 24 hours of reoxygenation and evaluated for apoptosis. In vivo, hindlimb ischemia/reperfusion injury was produced in mice by unilateral 2-hour tourniquet application followed by 24 hours of reperfusion. In three postinjury treatment groups (n = 7 mice/group), CoPP was administered intraperitoneally during ischemia, at the onset of reperfusion, or 1 hour later. Two control groups of mice with the same injury received phosphate-buffered saline (vehicle) or the HO-1 inhibitor, SnPP. Myocyte damage in the gastrocnemius and tibialis anterior muscles was determined by uptake of intraperitoneally delivered Evans blue dye (EBD), quantified by image analysis. On serial sections, inflammation was gauged by the mean myeloperoxidase staining intensity per unit area over the entirety of each muscle.

RESULTS

In MDSCs, a single exposure to CoPP increased HO-1 protein expression and enzyme activity, both of which were sustained for 96 hours. CoPP treatment of MDSCs reduced apoptotic cell populations by 55% after in vitro hypoxia/reoxygenation injury (from a mean of 57.3% apoptotic cells in vehicle-treated controls to 25.7% in CoPP-treated cells, mean difference 31.6%; confidence interval [CI], 28.1-35.0; p < 0.001). In the hindlimb ischemia/reperfusion model, CoPP delivered during ischemia produced a 38% reduction in myocyte damage in the gastrocnemius muscle (from 86.4% ± 7% EBD(+) myofibers in vehicle-treated, injured controls to 53.2% EBD(+) in CoPP-treated muscle, mean difference 33.2%; 95% CI, 18.3, 48.4; p < 0.001). A 30% reduction in injury to the gastrocnemius was seen with drug delivery at the onset of reperfusion (to 60.6% ± 13% EBD(+) with CoPP treatment, mean difference 25.8%; CI, 12.2-39.4; p < 0.001). In the tibialis anterior, however, myocyte damage was decreased only when CoPP was given at the onset of reperfusion, resulting in a 27% reduction in injury (from 78.8% ± 8% EBD(+) myofibers in injured controls to 58.3% ± 14% with CoPP treatment, mean difference 20.5%; CI, 6.1-35.0; p = 0.004). Delaying CoPP delivery until 1 hour after tourniquet release obviated the protective effect in both muscles. Mean MPO staining intensity per unit area, indicating the host inflammatory response, decreased by 27-34% across both the gastrocnemius and tibialis anterior muscles when CoPP was given either during ischemia or at the time of reperfusion. Delaying drug delivery until 1 hour after the start of reperfusion abrogated this antiinflammatory effect.

CONCLUSIONS

CoPP can decrease skeletal muscle damage when given early in the course of ischemia/reperfusion injury and also provide protection for regenerative stem cell populations.

CLINICAL RELEVANCE

Pharmacotherapy with HO-1 inducers, delivered in the field, on hospital arrival, or during trauma surgery, may improve preservation of muscle mass and muscle-inherent stem cells after severe ischemic limb injury.

Activity attenuates skeletal muscle fiber damage after ischemia and reperfusion

INTRODUCTION

In this investigation we aimed to determine whether: (1) physical activity protects rat skeletal muscle from ischemia/reperfusion (I/R) injury; and (2) continued activity after I/R improves the rate of healing.

METHODS

Rats were divided into sedentary or active (voluntary wheel running) groups. Active rats ran for 4 weeks before I/R or 4 weeks before plus 4 weeks after I/R.

RESULTS

Activity before I/R resulted in 73.2% less muscle damage (Evans blue dye inclusion). Sedentary and active rats had a similar decline in neural-evoked (∼ 99%) and directly stimulated (∼ 70%) in vivo muscle torque, and a similar reduction in junctophilin 1. Active rats produced 19% and 15% greater neural-evoked torque compared with sedentary rats at 14 and 28 days postinjury, respectively, although the rate of recovery appeared similar.

CONCLUSIONS

Activity protects against long-term muscle damage, but not short-term neural injury or excitation-contraction uncoupling. Continued activity neither accelerates nor hinders the rate of functional recovery.

Fat grafting to the hand in patients with Raynaud phenomenon: a novel therapeutic modality

BACKGROUND

Raynaud phenomenon causes progressively decreasing blood flow to the extremities, resulting from an imbalance between vasoconstriction and vasodilation. Treatment options include biofeedback, phosphodiesterase inhibitors, calcium channel inhibitors, botulinum toxin injection, or surgical sympathectomy. The authors propose fat grafting to the hands as a method to delay progression of the disease.

METHODS

Indications included symptomatic Raynaud phenomenon with failure of previous management. Fat is harvested from abdominal depots. Approximately 30 ml of decanted fat is injected by means of blunt cannulae: 10 to 15 ml in the dorsum of the hand, 2 to 3 ml in the snuffbox, 1 to 2 ml in each dorsal webspace, 3 to 4 ml along the superficial palmar arch, 1 to 2 ml in volar webspaces 2 to 4, and 2 to 3 ml in the first webspace. Patients underwent preoperative and postoperative laser speckle imaging study to assess changes in perfusion.

RESULTS

A total of 13 patients were treated (21 hands). Twelve patients had undergone prior botulinum toxin injection, and 11 patients had prior sympathectomies. Findings included reduced pain (average reduction, 6.86 of 10 to 2.38 of 10), fewer cold attacks, improved skin and soft-tissue texture, decrease in ulcerations, and patient-reported improved function. Three patients had no changes. Increased blood flow per imaging was noted in five of 11 hands tested. Six patients had decreased readings on laser imaging. None of the laser speckle imaging changes were statistically significant, and they did not correlate clinically. There were no major complications.

CONCLUSIONS

Preliminary results of fat grafting to the hands of patients with Raynaud phenomenon revealed improved symptomatology with evidence suggestive of measurably increased perfusion in some cases. Fat grafting may benefit the management of this patient population.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Accelerated functional recovery after skeletal muscle ischemia-reperfusion injury using freshly isolated bone marrow cells

BACKGROUND

Relatively little information exists regarding the usefulness of bone marrow-derived cells for skeletal muscle ischemia-reperfusion injury (I/R), especially when compared with I/R that occurs in other tissues. The objectives of this study were to evaluate the ability of freshly isolated bone marrow cells to home to injured skeletal muscle and to determine their effects on muscle regeneration.

MATERIALS AND METHODS

Freshly isolated lineage-depleted bone marrow cells (Lin(-) BMCs) were injected intravenously 2 d after I/R. Bioluminescent imaging was used to evaluate cell localization for up to 28 d after injury. Muscle function, the percentage of fibers with centrally located nuclei, and the capillary-to-fiber ratio were evaluated 14 d after delivery of either saline (Saline) or saline containing Lin(-) BMCs (Lin(-) BMCs).

RESULTS

Bioluminescence was higher in the injured leg than the contralateral control leg for up to 7 d after injection (P < 0.05) suggestive of cell homing to the injured skeletal muscle. Fourteen days after injury, there was a significant improvement in maximal tetanic torque (40% versus 22% deficit; P < 0.05), a faster rate of force production (+dP/dt) (123.6 versus 94.5 Nmm/S; P < 0.05), and a reduction in the percentage of fibers containing centrally located nuclei (40 versus 17%; P < 0.05), but no change in the capillary-to-fiber ratio in the Lin(-) BMC as compared with the Saline group.

CONCLUSIONS

The homing of freshly isolated BMCs to injured skeletal muscle after I/R is associated with an increase in functional outcomes.

Intramuscular transplantation and survival of freshly isolated bone marrow cells following skeletal muscle ischemia-reperfusion injury

BACKGROUND

Delayed treatment cellular therapies offer an attractive means to treat extremity injuries involving acute skeletal muscle ischemia-reperfusion injury (I/R). Bone marrow is a rich source of stem and progenitor cells with the potential to improve skeletal muscle regeneration. The extent to which bone marrow cells (BMCs) may be useful for I/R is not known. The purposes of this study were twofold: (1) to evaluate BMC survival following intramuscular injection 0, 2, 7, and 14 days after injury and (2) to determine whether BMCs improve functional recovery following I/R.

METHODS

Magnetic-activated cell sorting was used to isolate lineage-negative (Lin⁻) BMCs and enrich for stem and progenitor cells. To evaluate in vivo cell survival following I/R, Lin⁻ BMCs were injected intramuscularly 0, 2, 7, and 14 days after I/R, and bioluminescent imaging was performed for up to 28 days after cell injections. To assess their ability to improve muscle regeneration, intramuscular injections were performed 2 days after injury, and in vivo muscle function was assessed 14 days later.

RESULTS

Lin⁻ BMCs survived throughout the study period regardless of the timing of delivery. Intramuscular injection of Lin⁻ BMCs did not improve maximal isometric torque (300 Hz); however, both saline-injected and Lin⁻ BMC-injected muscles exhibited an increase in the twitch-tetanus ratio, suggesting that damage incurred with the intramuscular injections may have had deleterious consequences for functional recovery.

CONCLUSION

Although BMCs injected intramuscularly survived cell transplantation, they failed to improve muscle function following I/R. The ability of BMCs to persist in injured muscle following I/R lends to the possibility that with further development, their full potential can be realized.

Muscle-derived decellularised extracellular matrix improves functional recovery in a rat latissimus dorsi muscle defect model

PURPOSE

Craniofacial maxillary injuries represent nearly 30% of all battlefield wounds, often involving volumetric muscle loss (VML). The physical loss of muscle results in functional deficits and cosmetic disfigurement. Although surgical solutions are limited, advances in biomaterials offer great promise for the restoration of form and function following VML. The primary purpose of this study was to determine whether muscle function could be restored in a novel VML rat model using muscle-derived extracellular matrix (M-ECM).

METHODS

Ten percent of the mass of the latissimus dorsi (LD) was excised. Three groups were examined: 1) no repair of defect (DEF), 2) repair with M-ECM and 3) sham (all procedures except muscle excision). Four and 8 weeks post-surgery, the isometric contractile properties of the LD were assessed in situ and selected histological properties were evaluated.

RESULTS

The defect resulted in an initial reduction in peak isometric force (Po) of 30%. At 8 weeks the difference between DEF and sham was 20.5%. At the same time, M-ECM was only 8.4% below sham. Although the histological analysis revealed a narrow, but well-formed band of muscle running along the middle of the M-ECM, it was judged to be too small to account for the observed improvement in muscle force.

CONCLUSIONS

Repair of VML with M-ECM can dramatically improve muscle function independent of muscle regeneration by providing a physical bridge that accommodates force transmission across the injury site. This method of repair may provide an easily translatable surgical method for selected forms of VML.