Bilateral tripartite insertion of the fibularis (peroneus) brevis muscle: a case report / Inserción tripartita bilateral del músculo fibular corto: reporte de caso

SUMMARY: The fibularis brevis muscle typically inserts by a single long, robust, flat tendon upon the base of the fifth metatarsal. In this case report, we demonstrate two comparatively small accessory tendons of insertion in both the right and left limbs of an elderly cadaver. In each limb, the superior and inferior accessory tendons arose from the distal end of the main tendon of insertion to attach to, respectively, the shaft and neck of the fifth metatarsal. The bilateral presence of this comparatively rare condition is a new finding. Review of the literature reveals that these accessory tendons are most probably remnants of the inserting tendons of the atavistic muscle peroneus digiti minimi. The presence of this anomaly could affect reconstruction surgeries that utilize the inserting tendon of fibularis brevis, and treatment of avulsion fractures of the base of the fifth metatarsal.

RESUMEN: El músculo fibularis corto generalmente se inserta por un solo tendón largo, robusto y plano en la base del quinto metatarsiano. En este trabajo demostramos dos tendones accesorios de inserción comparativamente pequeños en ambos miembros inferiores de un cadáver de edad avanzada. En cada miembro inferior, los tendones accesorios superiores e inferiores surgieron de la porción distal del tendón principal de inserción para adherirse, respectivamente, al eje y al cuello del quinto metatarsiano. La presencia bilateral de éste músculo, comparativamente raro, es un nuevo hallazgo. La revisión de la literatura revela que estos tendones accesorios son probablemente remanentes de los tendones de inserción del músculo peroneus digiti minimi. La presencia de esta anomalía podría afectar las cirugías de reconstrucción que utilizan el tendón de inserción del músculo fibular corto, y el tratamiento de las fracturas por avulsión de la base del quinto hueso metatarsiano.

Change in the Pathologic Supraspinatus: A Three-Dimensional Model of Fiber Bundle Architecture within Anterior and Posterior Regions.

Supraspinatus tendon tears are common and lead to changes in the muscle architecture. To date, these changes have not been investigated for the distinct regions and parts of the pathologic supraspinatus. The purpose of this study was to create a novel three-dimensional (3D) model of the muscle architecture throughout the supraspinatus and to compare the architecture between muscle regions and parts in relation to tear severity. Twelve cadaveric specimens with varying degrees of tendon tears were used. Three-dimensional coordinates of fiber bundles were collected in situ using serial dissection and digitization. Data were reconstructed and modeled in 3D using Maya. Fiber bundle length (FBL) and pennation angle (PA) were computed and analyzed. FBL was significantly shorter in specimens with large retracted tears compared to smaller tears, with the deeper fibers being significantly shorter than other parts in the anterior region. PA was significantly greater in specimens with large retracted tears, with the superficial fibers often demonstrating the largest PA. The posterior region was absent in two specimens with extensive tears. Architectural changes associated with tendon tears affect the regions and varying depths of supraspinatus differently. The results provide important insights on residual function of the pathologic muscle, and the 3D model includes detailed data that can be used in future modeling studies.

Musculotendinous architecture of pathological supraspinatus: a pilot in vivo ultrasonography study.

Architectural changes associated with tendon tears of the supraspinatus muscle (SP) have not been thoroughly investigated in vivo with the muscle in relaxed and contracted states. The purpose of this study was to quantify the geometric properties within the distinct regions of SP in subjects with full-thickness tendon tears using an ultrasound protocol previously developed in our laboratory, and to compare findings with age/gender matched normal controls. Twelve SP from eight participants (6 male/2 female), mean age 57 ± 6.0 years, were investigated. Muscle geometric properties of the anterior region (middle and deep parts) and posterior region (deep part) were measured using image analysis software. Along with whole muscle thickness, fiber bundle length (FBL) and pennation angle (PA) were computed for architecturally distinct regions and/or parts. Pathologic SP was categorized according to the extent of the tear in the tendon (with or without retraction). In the anterior region, mean FBL of the pathologic SP was similar with normal controls; however, mean PA was significantly smaller in pathologic SP with retraction compared with normal controls, in the contracted state (P < 0.05). Mean FBL in the posterior region in both relaxed and contracted states was significantly shorter in the pathologic SP with retraction compared with normal controls (P < 0.05). Findings suggest FBL changes associated with tendon pathology vary between the distinct regions, and PA changes are related to whether there is retraction of the tendon. The ultrasound protocol may provide important information on architectural changes that may assist in decision making and surgical planning.

Retention of Pax3 expression in satellite cells of muscle spindles.

Intrafusal fibers within muscle spindles retain features characteristic of immaturity, unlike the larger and more numerous extrafusal fibers constituting the bulk of skeletal muscle. Satellite cells (SCs), myogenic progenitors, are detected on the surfaces of both intrafusal and extrafusal fibers, but little is known of spindle SCs. We have recently demonstrated that, like their extrafusal counterparts, SCs in muscle spindles of posthatch chickens express paired box transcription factor 7 (Pax7) protein. During vertebrate embryogenesis, myogenic progenitors express both Pax7 and Pax3 proteins. In postnatal mice, Pax3 appears in rare SC subsets, whereas Pax7 is expressed by all SCs within extrafusal fibers. Here we test the hypothesis that Pax3 protein maintains localized expression within SCs of muscle spindles. Immunohistochemical techniques were used to identify SCs by their Pax7 expression within anterior latissimus dorsi muscle excised from posthatch chickens of various ages. A greater percentage of SCs express Pax3 within intrafusal than extrafusal fibers at each age, and the proportion of SCs expressing Pax3 declines with aging. This is the first study to localize Pax3 expression in posthatch avian muscle and within SCs of muscle spindles. We suggest that Pax3-positive SCs are involved in fiber maintenance.

Nandrolone decanoate increases satellite cell numbers in the chicken pectoralis muscle.

The anabolic androgenic steroid nandrolone decanoate has minimal androgenic effects and, thus, is widely used to induce muscle hypertrophy in both patients and athletes. Although increases in satellite cell numbers and satellite cells giving rise to new myonuclei are associated with hypertrophy in many experimental models, the relationship between nandrolone and satellite cells is poorly understood. Here we test the hypothesis that nandrolone administration is associated with an increase in satellite cell numbers in muscle. Nandrolone was injected at weekly intervals for four weeks into the right pectoralis muscle of female white leghorn chickens aged 63 days post hatch. Age/size/sex matched control birds received saline injections. The contralateral pectoralis was excised for study from each control and nandrolone treated bird. An antibody against Pax7 and immunocytochemical techniques were used to identify satellite cells. Nandrolone significantly increased mean pectoralis mass by approximately 22%, and mean fiber diameter by about 24%. All satellite cell indices that were quantified increased significantly in chicken pectoralis with administration of nandrolone. Nandrolone injected birds had on average higher satellite cell frequencies (#SC nuclei/all nuclei within basal lamina), number of satellite cells per millimeter of fiber, and satellite cell concentrations (closer together). Myonuclei were further apart (less concentrated) in nandrolone injected muscle. However, an overall increase in myonuclear numbers was revealed by a significantly greater mean number of myonuclei per millimeter of fiber in nandrolone injected muscle. Our results suggest that satellite cells may be key cellular vectors for nandrolone induced muscle fiber hypertrophy.

Pax7 shows higher satellite cell frequencies and concentrations within intrafusal fibers of muscle spindles.

Intrafusal fibers within muscle spindles make up a small subpopulation of muscle fibers. These proprioceptive fibers differ from most extrafusal fibers because, even in maturity, their diameters remain small, and they retain expression of developmental myosins. Although both extrafusal and intrafusal fibers contain satellite cells (SCs), comparatively little is known about intrafusal SCs. Analyzing chicken fast-phasic posterior (PLD) and slow-tonic anterior (ALD) latissimus dorsi muscles, we show that SCs of both intrafusal and extrafusal fibers express Pax7. We further test the hypotheses that intrafusal fibers display parameters reflective of extrafusal immaturity. These hypotheses are that intrafusal fibers contain (a) higher SC frequencies (number of SC nuclei/all nuclei within basal lamina) and concentrations (closer together) and (b) smaller myonuclear domains than do adjacent extrafusal fibers. IHC techniques were applied to PLD and ALD muscles excised at 30 and 138 days posthatch. The hypotheses were validated, suggesting that intrafusal fibers have greater capacities for growth, regeneration, and repair than do adjacent extrafusal fibers. During maturation, extrafusal and intrafusal fibers show similar trends of decreasing SC frequencies and concentrations and increases in myonuclear domains. Thus, extrafusal and intrafusal fibers alike should exhibit reduced capacities for growth, regeneration, and repair during maturation.

Pax7 reveals a greater frequency and concentration of satellite cells at the ends of growing skeletal muscle fibers.

The main sites of longitudinal growth in skeletal muscle are the ends of the fibers. This study tests the hypothesis that satellite cells (SCs) are at a greater frequency (#SC nuclei/all nuclei within basal laminae) and concentration (closer together) within growing fiber ends of posthatch chicken pectoralis. SCs were localized by their Pax7 expression, and fiber ends were identified by their retention of neonatal myosin heavy chains and small cross-sectional profiles. Whereas SC frequency decreased from about 20% at 9 days posthatch to <5% at 115 days, fiber ends retained a frequency of approximately 16%. Calculated mean area of sarcolemma per SC revealed higher concentrations of SCs at fiber ends. There was also a strong inverse correlation between SC frequency and fiber profile cross-sectional size throughout development. This study suggests that SCs at fiber ends play a key role in the longitudinal growth of muscle fibers, and that fiber profile size may impact SC distribution.

The effect of glutamine on locomotor performance and skeletal muscle myosins following spinal cord injury in rats.

Following initial spinal cord injury (SCI), a cascade of pathological events, including oxidative stress, leads to secondary injury. Glutathione (GSH) plays a critical role in oxidant scavenging. Maintenance of GSH concentrations after SCI lessens secondary injury and improves recovery. Since glutamine promotes GSH synthesis, this nonessential amino acid was examined for therapeutic potential. Denervation alters the expression of myosin heavy chain (MHC) isoforms within skeletal muscles. The hypotheses of this study were that glutamine administration to SCI rats would lead to improved functional recovery and more preserved MHC phenotypes in representative locomotor muscles. Male Wistar rats were divided into four groups: healthy, sham with laminectomy, laminectomized SCI untreated, and laminectomized SCI treated with glutamine. Functional performance was measured weekly for 6 wk using Basso-Beattie-Bresnahan scale and angle board methods. MHC composition of rat soleus and extensor digitorum longus muscles was determined using SDS-PAGE. Glutamine-treated rats had significantly higher angle board scores (P < 0.001) and Basso-Beattie-Bresnahan scores (P < 0.01) than untreated SCI rats. Soleus of healthy rats contained 94% type 1 myosin isoform. Treated rats maintained 68%, which was significantly (P < 0.001) greater than 28% in untreated rats. The extensor digitorum longus of healthy rats contained 55% type 2b myosin. There was a significant (P < 0.001) decrease in this isoform following SCI, but no significant difference between treated and untreated groups. There were strong correlations between higher functional scores and more preserved MHC phenotypes. Our findings suggest glutamine improves functional recovery and helps preserve myosin profile by reducing secondary SCI, thereby maintaining more nerves.

Pattern of Pax7 expression during myogenesis in the posthatch chicken establishes a model for satellite cell differentiation and renewal.

The paired-box transcription factor Pax7 plays a critical role in the specification of satellite cells in mouse skeletal muscle. In the present study, the position and number of Pax7-expressing cells found in muscles of growing and adult chickens confirm the presence of this protein in avian satellite cells. The expression pattern of Pax7 protein, along with the muscle regulatory proteins MyoD and myogenin, was additionally elucidated in myogenic cultures and in whole muscle from posthatch chickens. In cultures progressing from proliferation to differentiation, the expression of Pax7 in MyoD+ cells declined as the cells began expressing myogenin, suggesting Pax7 as an early marker for proliferating myoblasts. At all time points, some Pax7+ cells were negative for MyoD, resembling the reserve cell phenotype. Clonal analysis of muscle cell preparations demonstrated that single progenitors can give rise to both differentiating and reserve cells. In muscle tissues, Pax7 protein expression was the strongest by 1 day posthatch, declining on days 3 and 6 to a similar level. In contrast, myogenin expression peaked on day 3 and then dramatically declined. This finding was accompanied by a robust growth in fiber diameter between day 3 and 6. The distinctions in Pax7 and myogenin expression patterns, both in culture and in vivo, indicate that while some of the myoblasts differentiate and fuse into myofibers during early stages of posthatch growth, others retain their reserve cell capacity.

Myonuclear domain size varies along the lengths of maturing skeletal muscle fibers.

In a skeletal muscle fiber, each myonucleus is responsible for gene expression in its surrounding cytoplasm. The region of cytoplasm associated with an individual myonucleus is termed myonuclear domain. However, little is known about domain size variation within individual muscle fibers. This study tests the hypothesis that myonuclear domains expressing neonatal myosin within end regions of maturing fibers will be smaller than domains elsewhere in the fibers. The model used is chicken pectoralis, where we have previously shown that during development repression of neonatal myosin radiates from the central region towards the fiber ends. Samples excised from birds aged nine through to 115 days after hatching were sectioned transversely. Using computer image analysis and immunocytochemistry, fiber profiles were classified as neonatal, transforming or adult. Each profile was also located in an adjacent dystrophin-labelled section, where myonuclei were visualized using haematoxylin and bisbenzamide. Variation in myonuclear length with age was not found to be significant (p = 0.925). Myonuclei were counted, and formulae used to calculate mean myonuclear domain size for each profile type. Myonuclear number/mm fiber was calculated to be adult (mean = 108.57 myonuclei/mm), transforming (65.82) and neonatal (25.23). Transforming profiles had significantly (p=0.027) more myonuclei/mm than neonatal, as did adult (p=0.005). Volume of cytoplasm/myonucleus was adult (mean = 16,132 microm3/myonucleus), transforming (12,899) and neonatal (8,130). Transforming and adult profiles had significantly (p<0.001) larger myonuclear domains than did neonatal profiles. Transforming and adult profiles did not differ in either myonuclei/mm (p=0.302) or volume of cytoplasm/myonucleus (p=0.413). This study demonstrates smaller domains at the terminal tips of maturing muscle fibers.