A finite element evaluation of the moment arm hypothesis for altered vertebral shear failure force

The mechanism of vertebral shear failure is likely a bending moment generated about the pars interarticularis by facet contact, and the moment arm length (MAL) between the centroid of facet contact and the location of pars interarticularis failure has been hypothesised to be an influential modulator of shear failure force. To quantitatively evaluate this hypothesis, anterior shear of C3 over C4 was simulated in a finite element model of the porcine C3–C4 vertebral joint with each combination of five compressive force magnitudes (0–60% of estimated compressive failure force) and three postures (flexed, neutral and extended). Bilateral locations of peak stress within C3's pars interarticularis were identified along with the centroids of contact force on the inferior facets. These measurements were used to calculate the MAL of facet contact force. Changes in MAL were also related to shear failure forces measured from similar in vitro tests. Flexed and extended vertebral postures respectively increased and decreased the MAL by 6.6% and 4.8%. The MAL decreased by only 2.6% from the smallest to the largest compressive force. Furthermore, altered MAL explained 70% of the variance in measured shear failure force from comparable in vitro testing with larger MALs being associated with lower shear failure forces. Our results confirmed that the MAL is indeed a significant modulator of vertebral shear failure force. Considering spine flexion is necessary when assessing low-back shear injury potential because of the association between altered facet articulation and lower vertebral shear failure tolerance.     

Comparative morphology of the pectoral fin spine of the Persian sturgeon Acipenser persicus,the Russian sturgeon Acipenser gueldenstaedtii,and the Starry sturgeon Acipenser stellatus in Iranian waters of the Caspian Sea

The morphological characteristics of the pectoral fin spine were compared in three species of sturgeon, the Persian sturgeon (Acipenser persicus), the Russian sturgeon (Acipenser gueldenstaedtii), and the Starry sturgeon (Acipenser stellatus), all sampled from the Caspian Sea. On the basis of morphological characters of the pectoral fin spine, 62.2% of the individuals were correctly classified into separate groups. The cluster analysis also divided the three species into two major subgroups. Acipenser persicus and A. gueldenstaedtii were grouped together, suggesting a similar evolutionary basis. Significant morphological heterogeneity in pectoral fin spine characteristics was observed among the three sturgeon species. Principal component analysis identified the largest differences were in the pectoral fin spine size and the angle between distal pectoral fin spine and the horizontal line (A°). The first and second principal components (PC1 and PC2) of all observations accounted for 64.19% and 14.33% of the total variation, respectively. The combination of all analyses showed the relevance of applying pectoral fin spine shape for interspecific distinction of the three species of sturgeons.     

The comparative morphology of epidermal glands in Pentatomoidea (Heteroptera)

The Heteroptera show a diversity of glands associated with the epidermis. They have multiple roles including the production of noxious scents. Here, we examine the cellular arrangement and cytoskeletal components of the scent glands of pentatomoid Heteroptera in three families, Pentatomidae (stink bugs), Tessaratomidae, and Scutelleridae (shield-backed bugs or jewel bugs). The glands are; (1) the dorsal abdominal glands, (2) the tubular glands of the composite metathoracic gland, and (3) the accessory gland component of the composite metathoracic gland. The dorsal abdominal glands are at their largest in nymphs and decrease in size in adults. The metathoracic gland is an adult-specific gland unit with a reservoir and multiple types of gland cells. The accessory gland is composed of many unicellular glands concentrated in a sinuous line across the reservoir wall. The lateral tubular gland is composed of two-cell units. The dorsal abdominal glands of nymphs are composed of three-cell units with a prominent cuticular component derived from the saccule cell sitting between the duct and receiving canal. The cuticular components that channel secretion from the microvilli of the secretory cell to the exterior differ in the three gland types. The significance of the numbers of cells comprising gland units is related to the role of cells in regenerating the cuticular components of the glands at moulting in nymphs.     

NF-κB Signaling Negatively Regulates Osteoblast Dedifferentiation during Zebrafish Bone Regeneration

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Assessment of the importance of fish predation versus copepod predation on life history traits of Daphnia hyalina

Daphnia hyalina is a cladoceran present throughthe whole year except for late summer in Maranhão,a meso-eutrophic reservoir in central Portugal. Apartfrom the influence of food, both vertebrate andinvertebrate predation pressures seem to have aneffect on D. hyalina population dynamics.Enclosure experiments were designed to assess therelative importance of both types of predation. Afterthe summer crash, D. hyalina reached highernumbers in the fishless enclosures than in the lakedespite of high predation pressure upon juveniles byAcanthocyclops robustus. Fish predation upon thelargest individuals, especially large egg bearingfemales, was responsible for the lower fertility ofthe open water population when compared with theenclosure population. In the enclosures an increase intail spine length was observed. The longer tail spineprobably offered protection from copepod predation,allowing at least some of the juveniles to coexistwith their potential predator and reach the adultstage, less susceptible to copepod predation.     

Computation models simulating notochordal cell extinction during early ageing of an intervertebral disc

Lower back pain due to intervertebral disc (IVD) degeneration is a prevalent problem which drastically affects the quality of life of millions of sufferers. Healthy IVDs begin with high populations of notochordal cells in the nucleus pulposus, while by the second stage of degeneration, these cells will be replaced by chondrocyte-like cells. Because the IVD is avascular, these cells rely on passive diffusion of nutrients to survive. It is thought that this transition in cell phenotype causes the shift of the IVD's physical properties, which impede the flow of nutrients. Our computational model of the IVD illustrates its ability to simulate the evolving chemical and mechanical environments occurring during the early ageing process. We demonstrate that, due to the insufficient nutrient supply and accompanying changes in physical properties of the IVD, there was a resultant exponential decay in the number of notochordal cells over time.     

Sensitivity of intervertebral joint forces to center of rotation location and trends along its migration path

Translational vertebral motion during functional tasks manifests itself in dynamic loci for center of rotation (COR). A shift of COR affects moment arms of muscles and ligaments; consequently, muscle and joint forces are altered. Based on posture- and level-specific trends of COR migration revealed by in vivo dynamic radiography during functional activities, it was postulated that the instantaneous COR location for a particular joint is optimized in order to minimize the joint reaction forces. A musculoskeletal multi-body model was employed to investigate the hypotheses that (1) a posterior COR in upright standing and (2) an anterior COR in forward flexed posture leads to optimized lumbar joint loads. Moreover, it was hypothesized that (3) lower lumbar levels benefit from a more superiorly located COR.The COR in the model was varied from its initial position in posterior-anterior and inferior-superior direction up to ±6 mm in steps of 2 mm. Movement from upright standing to 45° forward bending and backwards was simulated for all configurations. Joint reaction forces were computed at levels L2L3 to L5S1. Results clearly confirmed hypotheses (1) and (2) and provided evidence for the validity of hypothesis (3), hence offering a biomechanical rationale behind the migration paths of CORs observed during functional flexion/extension movement. Average sensitivity of joint force magnitudes to an anterior shift of COR was +6 N/mm in upright and −21 N/mm in 30° forward flexed posture, while sensitivity to a superior shift in upright standing was +7 N/mm and −8 N/mm in 30° flexion. The relation between COR loci and joint loading in upright and flexed postures could be mainly attributed to altered muscle moment arms and consequences on muscle exertion. These findings are considered relevant for the interpretation of COR migration data, the development of numerical models, and could have an implication on clinical diagnosis and treatment or the development of spinal implants.     

Morphing the feature-based multi-blocks of normative/healthy vertebral geometries to scoliosis vertebral geometries: development of personalized finite element models

Personalized Finite Element (FE) models and hexahedral elements are preferred for biomechanical investigations. Feature-based multi-block methods are used to develop anatomically accurate personalized FE models with hexahedral mesh. It is tedious to manually construct multi-blocks for large number of geometries on an individual basis to develop personalized FE models. Mesh-morphing method mitigates the aforementioned tediousness in meshing personalized geometries every time, but leads to element warping and loss of geometrical data. Such issues increase in magnitude when normative spine FE model is morphed to scoliosis-affected spinal geometry. The only way to bypass the issue of hex-mesh distortion or loss of geometry as a result of morphing is to rely on manually constructing the multi-blocks for scoliosis-affected spine geometry of each individual, which is time intensive. A method to semi-automate the construction of multi-blocks on the geometry of scoliosis vertebrae from the existing multi-blocks of normative vertebrae is demonstrated in this paper. High-quality hexahedral elements were generated on the scoliosis vertebrae from the morphed multi-blocks of normative vertebrae. Time taken was 3 months to construct the multi-blocks for normative spine and less than a day for scoliosis. Efforts taken to construct multi-blocks on personalized scoliosis spinal geometries are significantly reduced by morphing existing multi-blocks.     

小鼠脊髓背根神经节细胞共培养中P物质神经元的形态学观察

小鼠脊髓－背根神经节细胞在体外共培养状态Ｐ物质神经元的形态在国内尚未见文献报道。我们利用体外培养及免疫细胞化学方法对Ｐ物质神经元的胞体及突起形态做了观察,发现背根神经节中Ｐ物质免疫反应阳性的胞体为圆形成近似圆形,胞体直径大约为２８μｍ,突起较长,可有多级分枝。脊髓细胞中Ｐ物质反应阳性胞体多为圆形或椭圆形,胞体直径大约为１３μｍ左右,其突起有单极、双极和多极。在这种共培养状态下,Ｐ物质阳性反应纤维均比较纤细,但有的少见膨体,有的则膨体多见     

Ultraviolet absorbance of the mucus of a tropical damselfish: effects of ontogeny, captivity and disease

The ultraviolet (UV) absorbance of the mucus of a Great Barrier Reef damselfish Pomacentrus amboinensis was investigated with regard to ontogeny and time spent in captivity. The UV absorbance of P. amboinensis mucus increased with fish size and decreased with time spent in captivity. The wavelength of maximum absorbance of the mucus did not change with fish size, but shifted towards shorter wavelengths with increasing time spent in captivity. The UV absorbance of the mucus of fish with 'fin rot' was compared to that of similar healthy individuals, and a significant decrease in UV absorbance of unhealthy fish mucus was detected; no wavelength shifting occurred. Pomacentrus amboinensis appears to sequester mycosporine-like amino acids from the diet in order to protect epithelial tissues from UV damage, and decreases in UV absorbance in captive fish were probably due to insufficient dietary availability.