The extensor digitorum brevis as a muscle island flap

The use of the extensor digitorum brevis muscle as a local muscle island flap for the coverage of the soft-tissue defects in the region of the lateral malleolus is presented. The anatomy of the muscle, the donor dissection, and the utilization of the extensor digitorum brevis muscle as a local muscle flap in the lower extremity are discussed. This flap was used successfully in a patient with a wound over the lateral malleolus and ankle.     

Extensor digitorum brevis as an island flap in the reconstruction of soft-tissue defects in the lower limb

The extensor digitorum brevis island flap is a versatile and robust flap able to provide adequate bulk and coverage in soft-tissue defects of the lower limb. The donor-site deformity is limited to the necessary scar needed to approach and rotate the muscle. An anatomic study was performed in 10 fresh cadavers and consisted of two parts: study of the muscle flap itself, and examination of skin vascularization. Methylene blue and Salmon's mass (radiopaque) were injected through the three main arteries of the leg. Muscle and cutaneous staining were noted. Clinical applications of this flap are reported. These resulted in successful healing of the defect with good aesthetic and functional results on both recipient and donor sites. Long-term follow-up was maintained for up to 21 months.     

The distally pedicled peroneus brevis muscle flap: a new flap for the lower leg

Defects of the skin and soft tissue in the region of the lateral malleolus of the ankle and the Achilles tendon, resulting in exposed bone, tendons, or osteosynthetic material, cannot be covered with free skin transplants. Local or free flaps must be employed. The authors present the construction of a peroneus brevis muscle flap with a distal pedicle as a useful alternative. Between 1993 and 1999, distal pedicled peroneus brevis muscle flaps were used in 19 patients with various types of defects. During construction of the flap, both the long peroneal muscle and the peroneal artery remained intact. In the region of the distal third of the fibula, consistently arranged branches run from the artery into the muscle, and these form the distal pedicle. The proximal portion of the muscle can be transposed distally and easily extends to the tip of the fibula and the attachment of the Achilles tendon to the calcaneus. Primary healing occurred in 16 patients undergoing flap construction. Donor-site morbidity was mostly limited to the donor-site scar. The distally pedicled peroneus brevis muscle flap is a reliable means for covering defects in the lower leg. This form of muscle flap has not yet been described in the known literature. In the authors' opinion, this flap constitutes a logical and valuable extension of local flap procedures for plastic surgery in the distal leg region.     

Extensor digitorum brevis free flap: anatomic study and further clinical applications

The extensor digitorum brevis muscle flap is reliable, safe, and can be used either as a pedicle or as a free flap with minimal donor site morbidity. To increase the existing knowledge of this flap and to establish further anatomic basis for the design and elevation of the extensor digitorum brevis flap, 26 specimens from 13 fresh cadavers were dissected under 3.5x loupes. The lateral tarsal artery was found to be the main blood supply to the muscle. It has an average diameter of 1.83+/-0.35 mm and a length of 1.89+/-0.69 cm. The dorsalis pedis artery has, at the level of the lateral tarsal artery takeoff, a diameter of 3.25+/-0.62 mm. From this point to the origin of the deep plantar branch, the dorsalis pedis artery has minimal branching, and the surgeon has available an artery homogeneous in diameter that is 6.77+/-0.99 cm in length. Related neurovascular structures (anterior tibial artery and the venae comitantes, dorsalis pedis and first dorsal metatarsal artery, and deep peroneal nerve) were also studied. A safe and reliable harvesting technique and the "T interposed extensor digitorum brevis" technique for sparing the anterior tibial artery are presented, as are clinical case examples on the use of this flap as a flow-through, extensor digitorum brevis-vascularized nerve graft, a combined extensor digitorum brevis-deep peroneal nerve graft, and a bilobed extensor digitorum brevis-dorsalis pedis fasciosubcutaneous free flap.     

Formation of extensor digitorum muscle proportions before and after birth

Studies on the formation of the extensor digitorum muscle morphological characteristics were carried out on material of 85 human fetuses (42 males and 43 females), 16 to 36 weeks old, and 45 adults (31 males and 14 females). Intermediary conclusions were drawn on probable changes occurring in the morphological formation of the muscle after birth, as a result of comparing proportions of the muscle at the fetal stage with its form in adults. In this work, the anthropometric method of study and statistical analysis of results have been applied. Analysis of the results in the fetal group has shown that all metrical characteristics of the muscle reach their maximum values at the end of the investigated ontogenetic space. This is, naturally, a consequence of evolution and growth of all fetal body measures, including elongation of forearms. However, the evolution of the individual muscle characteristics is not regular and though the direction of this growth is similar, its extent varies, and also differs slightly in sexual groups. Comparison of the values of muscle indices for 9 month old fetuses with the same indices for adults shows that relative dimensions of all investigated muscular characteristics decrease during the post-natal period except the relative length of the tendon.     

The human extensor digitorum profundus muscle with comments on the evolution of the primate hand

Forelimb dissections on 14 genera of anthropoids including humans and 17 cases of human aneuploids has revealed a high incidence of “atavistic” musculature (Barash et al., 1970;Aziz, 1981a) in the aneuploids. The phenotypic specificity of this aneuploid musculature clearly manifests developmental retardation and instability (Shapiro, 1983) revealing not only the likely course of embryonic myogenesis in chromosomally normal humans (Cihak, 1972, 1977) but also information relevant to ontogenetic and evolutionary changes. The extensor digitorum profundus proprius complex is particularly illustrative of these characteristics of aneuploid musculature. Our examination of the variation of this muscle complex in human aneuploids and between primate genera reveals how normal ontogeny may proceed, as well as the morphological basis for the evolutionary changes in hand structure and function amongst Primates. We also consider the phylogenetic and functional significance of changes in the extensor digitorum profundus proprius with reference to the divergent locomotory and manipulative capabilities and behavior of Primates.     

Organogenesis of the mouse extensor digitorum logus muscle: a quantitative study

A quantitative analysis of the pattern of development and growth of the fetal extensor digitorum longus muscle of the 129 ReJ mouse was carried out in spaced, serial ultrathin sections with computer-assisted morphometry. Muscle from 12-, 14-, 16-, and 18-day in utero mice and from newborn and 5-day postnatal mice was analyzed to determine age-related changes in such factors as the maximal girth and length of the muscle, the number of myotubes, the "cluster" frequency, and the diameters and lengths of the myotubes and muscle units. A distinct temporal pattern of development was established. It was quantitatively determined that a delay less than or equal to 2 days occurs between the formation of primary myotubes (present at 12 days in utero) and secondary myotubes (present at 16 days in utero). By 16 days in utero, groups of myotubes, consisting of one primary myotube and a variable number of secondary myotubes, form "clusters" surrounded by a common basal lamina. Morphometric analyses of diameter distributions establish that most, if not all, secondary-generation myotubes are formed in association with larger, more mature myotubes. Quantitative data support the hypothesis (Ontell and Kozeka, 1984) that cluster formation and cluster dispersion occur simultaneously, beginning sometime between 16 and 18 days in utero. By 18 days in utero, the adult number of myofibers is present in the developing muscle mass. Analyses of lengths and diameters of the same fibers establish that the pattern of growth of the last-formed myotubes of the developing muscle mass is different from that of myotubes formed earlier in development.     

Quantitative morphometric analyses of the exercised extensor digitorum longus muscle of the mouse

The metric properties of several important components of muscle, the capillaries, the myonuclei and also the cross-sectional areas of type I and type II fibres in the extensor digitorum longus muscle of the mouse have been studied using techniques appropriate for anisotropic tissues. Myonuclear volume density (Nv) was found to be increased by 70% whilst capillary length density (Lv) was increased by 50%. The results were analysed using multivariate statistical analysis (MANOVA) which is necessary for the multiple comparisons which inevitably occur in any morphometric investigation. The mitochondrial distribution within type I fibres was analysed using two-way ANOVA to study the effect of exercise on the mitochondrial contents of the inner, intermediate and outer zones of the muscle fibre. Significant differences in the mitochondrial content in the various zones were found. Exercise was found to increase mitochondrial contents in all three zones.     

Dissociated flexor digitorum brevis myofiber culture system--a more mature muscle culture system

Considerable knowledge regarding skeletal muscle physiology and disease has been gleaned from cultured myoblastic cell lines or isolated primary myoblasts. Such muscle cultures can be induced to differentiate into multinucleated myotubes that become striated. However they in general do not fully mature and therefore do not model mature muscle. Contrastingly, fresh and cultured dissociated adult mouse flexor digitorum brevis (FDB) myofibers have been studied for many years. We aimed to investigate the possibility of using the FDB myofiber culture system for drug screening and thus long-term cultures of enzymatically dissociated FDB myofibers were established in 96-well plates. Ca2+ handling experiments were used to investigate the functional state of the myofibers. Imaging of intracellular Ca2+ during electric field stimulation revealed that calcium handling was maintained throughout the culture period of at least 8 days. Western blot and immunostaining analysis showed that the FDB cultures maintained expression of mature proteins throughout the culture period, including alpha-sarcoglycan, dystrophin, fast myosin heavy chain and skeletal muscle alpha-actin. The high levels of the fetal proteins cardiac alpha-actin and utrophin, seen in cultured C2C12 myotubes, were absent in the FDB cultures. The expression of developmentally mature proteins and the absence of fetal proteins, in addition to the maintenance of normal calcium handling, highlights the FDB culture system as a more mature and perhaps more relevant culture system for the study of adult skeletal muscle function. Moreover, it may be a useful system for screening therapeutic agents for the treatment of skeletal muscle disorders.     

Characterization of the isolated rat flexor digitorum brevis for the study of skeletal muscle phosphorylase kinase phosphorylation

The flexor digitorum brevis skeletal muscle, a nearly homogeneous fast-twitch oxidative glycolytic fiber type, has been examined for its suitability to explore the regulation of phosphorylase kinase by multisite phosphorylation. A characterization of the adrenergic response of glycogenolytic enzymes, together with the previous data on contractile properties (Carlsen, R. C., Larson, D. B., and Walsh, D. A. (1985) Can. J. Physiol. Pharm. 63, 958-965), has demonstrated that this muscle is stably maintained for the several hours necessary for phosphorylation studies. The phosphorylase kinase in this muscle is primarily the alpha' isozyme, suggesting that the alpha versus alpha' isozyme distribution in muscle is related more to oxidative capacity than to fiber contractile characteristics. Using this muscle system, beta-adrenergic activation of phosphorylase kinase was observed to occur with concomitant phosphorylation of both the alpha' and beta subunits, with the total in the alpha' subunit being approximately 3-fold greater. Similarly, deactivation, following initial adrenergic activation, occurred concomitantly with the dephosphorylation of the two subunits. These results are compatible with the conclusions drawn from previous studies of the isolated enzyme and of the enzyme in perfused rat cardiac muscle, that both alpha' (or alpha) and beta subunit phosphorylation regulate phosphorylase kinase activity.     

Sphingosine 1-phosphate protects mouse extensor digitorum longus skeletal muscle during fatigue

Sphingomyelin derivatives exert various second messenger actions in numerous tissues. Sphingosine (SPH) and sphingosine 1-phosphate (S1P) are two major sphingomyelin derivatives present at high levels in blood. The aim of the present work was to investigate whether S1P and SPH exert relevant actions in mouse skeletal muscle contractility and fatigue. Exogenous S1P and SPH administration caused a significant reduction of tension decline during fatigue of extensor digitorum longus muscle. Final tension after the fatiguing protocol was 40% higher than in untreated muscle. Interestingly, N,N-dimethylsphingosine, an inhibitor of SPH kinase (SK), abolished the effect of supplemented SPH but not that of S1P, suggesting that SPH acts through its conversion to S1P. Moreover, SPH was not effective in Ca²⁺-free solutions, in agreement with the hypothesis that SPH action is dependent on its conversion to S1P by the Ca²⁺-requiring enzyme SK. In contrast to SPH, S1P produced its positive effects on fatigue in Ca²⁺-free conditions, indicating that S1P action does not require Ca²⁺ entry and most likely is receptor mediated. The effects of S1P could be ascribed in part to its ability to prevent the reduction (–20 mV) of action potential amplitude caused by fatigue. In conclusion, these results indicate that extracellular S1P has protective effects during the development of muscle fatigue and that the extracellular conversion of SPH to S1P may represent a rheostat mechanism to protect skeletal muscle from possible cytotoxic actions of SPH. sphingosine kinase; action potential; sphingosine     

Catalase-positive microperoxisomes in rat soleus and extensor digitorum longus muscle fiber types

The size, distribution, and content of catalase-reactive microperoxisomes were studied cytochemically in slow-twitch oxidative (SO), fast-twitch oxidative glycolytic (FOG), and fast-twitch glycolytic (FG) fibers of soleus and extensor digitorum longus (EDL) rat muscles. Fiber types were classified on the basis of mitochondrial content and distribution, Z-band widths, and myofibril size and shape. Microperoxisomes were generally located between myofibrils at the I-bands. The absence of crystalloid inclusions prevented positive identification of microperoxisomes in nonreacted and aminotriazole-inhibited muscles. EDL and soleus SO fibers possessed the largest microperoxisomes, whereas FOG and FG fibers of the EDL contained small- to medium-sized microperoxisomes. Comparing either microperoxisome number per muscle fiber area or microperoxisome area per fiber area revealed significant differences between fiber types with this ranking: soleus SO greater than EDL SO greater than EDL FOG greater than EDL FG. The present observations demonstrate that the content of catalase-positive microperoxisomes is greatest in the oxidative muscle fiber types. These cytochemical findings account for the higher catalase activity in homogenates of soleus muscles as compared to that of EDL muscles, because the soleus contains more oxidative fibers than EDL.     

The histochemical profile of the rat extensor digitorum longus muscle differentiates after birth and dedifferentiates in senescence

Age dependent motor unit dedifferentiation is a key component of impaired muscle function in advanced age. Here, we tested the hypothesis that rat muscle histochemical profile during the lifespan of an individual has an age-specific pattern since comprehensive longitudinal studies of muscle differentiation after birth and dedifferentiation in advanced age are scarce. Our results show that extensor digitorum longus muscle (EDL) is comprised only of two fiber types after birth, type slow-oxidative (SO) and type SDH-intermediate (SDH-INT), the latter being indicative for the presence of polyneuronal innervation. In contrast to the constantly growing cross-sectional area of the muscle fibers, a dramatic decrease in SDH-INT proportion occurs between day 14 and 21 after birth resulting in a complete loss of fiber type SDH-INT at the age of 90 days (p<0.05). At the age of 270 days, the fiber type composition of rat EDL dedifferentiates as shown by the reappearance of the SDH-INT type with a further increase at the age of 540 days (p<0.05). These changes in histochemical fiber type spectra are brought about by fiber type conversion within the fast twich fibers. The findings of the present study provide further evidence that fiber type conversion is a basic mechanism leading to motor unit differentiation and dedifferentiation during ontogenesis. Fiber type conversion shows a distinct time specific pattern and is also characteristic for motor unit regeneration after peripheral nerve repair. Factors that influence fiber type conversion and thereby motor unit organization may provide a future therapeutic option to enhance the regenerative capacity of motor units.     

Denervated muscle fibers explain the deficit in specific force following reinnervation of the rat extensor digitorum longus muscle

The authors tested the hypothesis that, after denervation and reinnervation of skeletal muscle, observed deficits in specific force can be completely attributed to the presence of denervated muscle fibers. The peroneal nerve innervating the extensor digitorum longus muscle in rats was sectioned and the distal stump was coapted to the proximal stump, allowing either a large number of motor axons (nonreduced, n = 12) or a drastically reduced number of axons access to the distal nerve stump (drastically reduced, n = 18). A control group of rats underwent exposure of the peroneal nerve, without transection, followed by wound closure (control, n = 9). Four months after the operation, the maximum tetanic isometric force (Fo) of the extensor digitorum longus muscle was measured in situ and the specific force (sFo) was calculated. Cross-sections of the muscles were labeled for neural cell adhesion molecule (NCAM) protein to distinguish between innervated and denervated muscle fibers. Compared with extensor digitorum longus muscles from rats in the control (295 +/- 11 kN/m2) and nonreduced (276 +/- 12 kN/m2) groups, sFo of the extensor digitorum longus muscles from animals in the drastically reduced group was decreased (227 +/- 15 kN/m2, p < 0.05). The percentage of denervated muscle fibers in the extensor digitorum longus muscles from animals in the drastically reduced group (18 +/- 3 percent) was significantly higher than in the control (3 +/- 1 percent) group, but not compared with the nonreduced (9 +/- 2 percent) group. After exclusion of the denervated fibers, sFo did not differ between extensor digitorum longus muscles from animals in the drastically reduced (270 +/- 20 kN/m2), nonreduced (301 +/- 13 kN/m2), or control (303 +/- 10 kN/m2) groups. The authors conclude that, under circumstances of denervation and rapid reinnervation, the decrease in sFo of muscle can be attributed to the presence of denervated muscle fibers.     

The influence of passive stretch on the growth and protein turnover of the denervated extensor digitorum longus muscle

At 7 days after cutting the sciatic nerve, the extensor digitorum longus muscle was smaller and contained less protein than its innervated control. Correlating with these changes was the finding of elevated rates of protein degradation (measured in vitro) in the denervated tissue. However, at this time, rates of protein synthesis (measured in vitro) and nucleic acid concentrations were also higher in the denervated tissue, changes more usually associated with an active muscle rather than a disused one. These anabolic trends have, at least in part, been explained by the possible greater exposure of the denervated extensor digitorum longus to passive stretch. When immobilized under a maintained influence of stretch the denervated muscle grew to a greater extent. Although this stretch-induced growth appeared to occur predominantly through a stimulation of protein synthesis, it was opposed by smaller increases in degradative rates. Nucleic acids increased at a similar rate to the increase in muscle mass when a continuous influence of stretch was imposed on the denervated tissue. In contrast, immobilization of the denervated extensor digitorum longus in a shortened unstretched state reversed most of the stretch-induced changes; that is, the muscle became even smaller, with protein synthesis decreasing to a greater extent than breakdown after the removal of passive stretch. The present investigation suggests that stretch will promote protein synthesis and hence growth of the extensor digitorum longus even in the absence of an intact nerve supply. However, some factor(s), in addition to passive stretch, must contribute to the anabolic trends in this denervated muscle.     

Gamma irradiation prevents compensatory hypertrophy of overloaded mouse extensor digitorum longus muscle.

Mouse extensor digitorum longus (EDL) muscle was subjected to a dose of gamma irradiation that causes reproductive death of satellite cells and/or to chronic compensatory overload, achieved by removal of the distal portion of the tibialis anterior muscle. Four weeks later the mass, fiber type percentage, and fiber size of the EDL muscle were measured. Both the irradiated + overloaded and the irradiated only EDL muscles were significantly lighter and contained significantly smaller fibers than untreated muscle or muscle subjected to chronic overload only. Overload muscle, whether irradiated or not, had a larger percentage of type IIx fibers and a smaller percentage of type IIb fibers than muscle that had not been overloaded. The results confirm that satellite cell proliferation is a prerequisite for muscle hypertrophy induced by synergist incapacitation, but it appears not to be required for the maintenance of, or change in, normal muscle fiber myosin heavy chain phenotype expression.