An unusual presentation of a malignant jejunal tumor and a different management strategy

BACKGROUND: Malignant small bowel tumors are very rare and leiomyosarcoma accounts for less than 15% of the cases. Management of these tumors is challenging in view of nonspecific symptoms, unusual presentation and high incidence of metastasis. In this case report, an unusual presentation of jejunal sarcoma and management of liver metastasis with radiofrequency ablation (RFA) is discussed. CASE PRESENTATION: A 45-year-old male presented with anemia and features of small bowel obstruction. Operative findings revealed a mass lesion in jejunum with intussusception of proximal loop. Resection of bowel mass was performed. Histopathological findings were suggestive of leiomyosarcoma. After 3-years of follow-up, the patient developed recurrence in infracolic omentum and a liver metastasis. The omental mass was resected and liver lesion was managed with radiofrequency ablation. CONCLUSION: Jejunal leiomyosarcoma is a rare variety of malignant small bowel tumor and a clinical presentation with intussusception is unusual. We suggest that an aggressive management approach using a combination of surgery and a newer technique like RFA can be attempted in patients with limited metastatic spread to liver to prolong the long-term survival in a subset of patients.     

Trabecular bone strains around a dental implant and associated micromotions—A micro-CT-based three-dimensional finite element study

The first objective of this computational study was to assess the strain magnitude and distribution within the three-dimensional (3D) trabecular bone structure around an osseointegrated dental implant loaded axially. The second objective was to investigate the relative micromotions between the implant and the surrounding bone. The work hypothesis adopted was that these virtual measurements would be a useful indicator of bone adaptation (resorption, homeostasis, formation).In order to reach these objectives, a μCT-based finite element model of an oral implant implanted into a Berkshire pig mandible was developed along with a robust software methodology. The finite element mesh of the 3D trabecular bone architecture was generated from the segmentation of μCT scans. The implant was meshed independently from its CAD file obtained from the manufacturer. The meshes of the implant and the bone sample were registered together in an integrated software environment. A series of non-linear contact finite element (FE) analyses considering an axial load applied to the top of the implant in combination with three sets of mechanical properties for the trabecular bone tissue was devised. Complex strain distribution patterns are reported and discussed. It was found that considering the Young’s modulus of the trabecular bone tissue to be 5, 10 and 15 GPa resulted in maximum peri-implant bone microstrains of about 3000, 2100 and 1400. These results indicate that, for the three sets of mechanical properties considered, the magnitude of maximum strain lies within an homeostatic range known to be sufficient to maintain/form bone. The corresponding micro-motions of the implant with respect to the bone microstructure were shown to be sufficiently low to prevent fibrous tissue formation and to favour long-term osseointegration.     

Species loss of stoneflies (Plecoptera) in the Czech Republic during the 20th century

1. Rapid expansion and intensification of anthropogenic activities in the 20th century has caused profound changes in freshwater assemblages. Unfortunately, knowledge of the extent and causes of species loss (SL) is limited due to the lack of reliable historical data. An unusual data set allows us to compare changes in the most sensitive of aquatic insect orders, the Plecoptera, at some 170 locations in the Czech Republic between two time periods, 1955–1960 and 2006–2010. Historical data (1890–1911) on assemblages of six lowland rivers allow us to infer even earlier changes. 2. Regional stonefly diversity decreased in the first half of the 20th century. Streams at lower altitudes lost a substantial number of species, which were never recovered. In the second half of the century, large‐scale anthropogenic pressure caused SL in all habitats, leading to a dissimilarity of contemporary and previous assemblages. The greatest changes were found at sites affected by organic pollution and a mixture of organic pollution and channelisation or impoundment. Colonisation of new habitats was observed in only three of the 80 species evaluated. 3. Species of moderate habitat specialisation and tolerance to organic pollution were most likely to be lost. Those with narrow specialisations in protected habitats were present in both historical and contemporary collections. 4. Contemporary assemblages are the consequence of more than a 100 years of anthropogenic impacts. In particular, streams at lower altitude and draining intensively exploited landscapes host a mere fragment of the original species complement. Most stonefly species are less frequently present than before, although their assemblages remain almost intact in near‐natural mountain streams. Our analyses demonstrate dramatic restriction of species ranges and, in some cases, apparent changes in altitudinal preference throughout the area.     

Moderate alcohol consumption is associated with better endothelial function: a cross sectional study

Background

Natural heterologous valved conduits with a diameter greater than 22 mm that can be used for right ventricular outflow tract reconstruction in adults are not commercially available. The purpose of this study was to measure by ultrasonography the maximum diameter of the distended jugular veins of horses and cattle, respectively, to identify a population of animals that would be suitable for post-mortem collection of jugular veins at sizes greater than 22 mm.

Methods

The study population included 60 Warmblood horses, 25 Freiberger horses, 20 Brown Swiss cows, and 20 Holstein cows (including 10 Holstein and 10 Red Holstein). The maximum cross-sectional diameter of the distended jugular veins was measured at a location half-way between the mandibular angle and the thoracic inlet. The thoracic circumference (heart girth length) was used as a surrogate of body size. The jugular vein diameters of the different populations were compared by analysis of variance and the association between heart girth length and jugular vein diameter was determined in each of the four study populations by linear regression analysis.

Results

There was considerable individual variation of jugular vein diameters within each of the four study populations. There was no statistically significant relationship between thoracic circumference and jugular vein diameter in any of the populations. The jugular vein diameters of Brown Swiss cows were significantly larger than those of any of the other populations. Warmblood horses had significantly larger jugular vein diameters compared to Freiberger horses.

Conclusion

The results of this study suggest that the production of bovine or equine xenografts with diameters of greater than 22 mm would be feasible. Differences between species and breeds need to be considered. However, prediction of the jugular vein diameter based on breed and heart girth length in an individual animal is inaccurate.     

Fast and accurate specimen-specific simulation of trabecular bone elastic modulus using novel beam-shell finite element models

Elastic modulus and strength of trabecular bone are negatively affected by osteoporosis and other metabolic bone diseases. Micro-computed tomography-based beam models have been presented as a fast and accurate way to determine bone competence. However, these models are not accurate for trabecular bone specimens with a high number of plate-like trabeculae. Therefore, the aim of this study was to improve this promising methodology by representing plate-like trabeculae in a way that better reflects their mechanical behavior. Using an optimized skeletonization and meshing algorithm, voxel-based models of trabecular bone samples were simplified into a complex structure of rods and plates. Rod-like and plate-like trabeculae were modeled as beam and shell elements, respectively, using local histomorphometric characteristics. To validate our model, apparent elastic modulus was determined from simulated uniaxial elastic compression of 257 cubic samples of trabecular bone (4mm×4mm×4mm; 30μm voxel size; BIOMED I project) in three orthogonal directions using the beam-shell models and using large-scale voxel models that served as the gold standard. Excellent agreement (R(2)=0.97) was found between the two, with an average CPU-time reduction factor of 49 for the beam-shell models. In contrast to earlier skeleton-based beam models, the novel beam-shell models predicted elastic modulus values equally well for structures from different skeletal sites. It allows performing detailed parametric analyses that cover the entire spectrum of trabecular bone microstructures.     

Numerical simulation of the insertion process of an uncemented hip prosthesis in order to evaluate the influence of residual stress and contact distribution on the stem initial stability

The long-term success of a cementless total hip arthroplasty depends on the implant geometry and interface bonding characteristics (fit, coating and ingrowth) and on stem stiffness. This study evaluates the influence of stem geometry and fitting conditions on the evolution and distribution of the bone–stem contact, stress and strain during and after the hip stem insertion, by means of dynamic finite element techniques. Next, the influence of the mechanical state (bone–stem contact, stress and strain) resulted from the insertion process on the stem initial resistance to subsidence is investigated. In addition, a study on the influence of bone–stem interface conditions (friction) on the insertion process and on the initial stem stability under physiological loading is performed. The results indicate that for a stem with tapered shape the contact in the proximal part of the stem was improved, but contact in the calcar region was achieved only when extra press-fit conditions were considered. Changes in stem geometry towards a more tapered shape and extra press fit and variation in the bone–stem interface conditions (contact amount and high friction) led to a raise in the total insertion force. A direct positive relationship was found between the stem resistance to subsidence and stem geometry (tapering and press fit), bone–stem interface conditions (bone–stem contact and friction interface) and the mechanical status at the end of the insertion (residual stress and strain). Therefore, further studies on evaluating the initial performance of different stem types should consider the parameters describing the bone–stem interface conditions and the mechanical state resulted from the insertion process.     

Intragenic duplication and divergence in the spectrin superfamily of proteins

Many structural, signaling, and adhesion molecules contain tandemly repeated amino acid motifs. The alpha-actinin/spectrin/dystrophin superfamily of F-actin-crosslinking proteins contains an array of triple alpha-helical motifs (spectrin repeats). We present here the complete sequence of the novel beta-spectrin isoform beta(Heavy)- spectrin (beta H). The sequence of beta H supports the origin of alpha- and beta-spectrins from a common ancestor, and we present a novel model for the origin of the spectrins from a homodimeric actin-crosslinking precursor. The pattern of similarity between the spectrin repeat units indicates that they have evolved by a series of nested, nonuniform duplications. Furthermore, the spectrins and dystrophins clearly have common ancestry, yet the repeat unit is of a different length in each family. Together, these observations suggest a dynamic period of increase in repeat number accompanied by homogenization within each array by concerted evolution. However, today, there is greater similarity of homologous repeats between species than there is across repeats within species, suggesting that concerted evolution ceased some time before the arthropod/vertebrate split. We propose a two-phase model for the evolution of the spectrin repeat arrays in which an initial phase of concerted evolution is subsequently retarded as each new protein becomes constrained to a specific length and the repeats diverge at the DNA level. This evolutionary model has general applicability to the origins of the many other proteins that have tandemly repeated motifs.      

Comparisons of the molecular evolutionary process at rbcL and ndhF in the grass family (Poaceae)

We examine rate heterogeneity among evolutionary lineages of the grass family at two plasmid loci, ndhF and rbcL, and we introduce a method to determine whether patterns of rate heterogeneity are correlated between loci. We show both that rates of synonymous evolution are heterogeneous among grass lineages and that are heterogeneity is correlated between loci at synonymous sites. At nonsynonymous sites, the pattern of rate heterogeneity is not correlated between loci, primarily due to an aberrant pattern of rate heterogeneity at nonsynonymous sites of rbcL. We compare patterns of synonymous rate heterogeneity to predictors based on the generation time effect and the speciation rate hypotheses. Although there is some evidence for generation time effects, neither generation time effects nor speciation rates appear to be sufficient to explain patterns of rate heterogeneity in the grass plastid sequences.      

Relation between subject-specific hip joint loading, stress distribution in the proximal femur and bone mineral density changes after total hip replacement

In the prediction of bone remodelling processes after total hip replacement (THR), modelling of the subject-specific geometry is now state-of-the-art. In this study, we demonstrate that inclusion of subject-specific loading conditions drastically influences the calculated stress distribution, and hence influences the correlation between calculated stress distributions and changes in bone mineral density (BMD) after THR.For two patients who received cementless THR, personalized finite element (FE) models of the proximal femur were generated representing the pre- and post-operative geometry. FE analyses were performed by imposing subject-specific three-dimensional hip joint contact forces as well as muscle forces calculated based on gait analysis data. Average values of the von Mises stress were calculated for relevant zones of the proximal femur. Subsequently, the load cases were interchanged and the effect on the stress distribution was evaluated. Finally, the subject-specific stress distribution was correlated to the changes in BMD at 3 and 6 months after THR.We found subject-specific differences in the stress distribution induced by specific loading conditions, as interchanging of the loading also interchanged the patterns of the stress distribution. The correlation between the calculated stress distribution and the changes in BMD were affected by the two-dimensional nature of the BMD measurement.Our results confirm the hypothesis that inclusion of subject-specific hip contact forces and muscle forces drastically influences the stress distribution in the proximal femur. In addition to patient-specific geometry, inclusion of patient-specific loading is, therefore, essential to obtain accurate input for the analysis of stress distribution after THR.     

Construction and Characterization of a Magnaporthe grisea Bacterial Artificial Chromosome Library

Diaz-Perez, S. V., Crouch, V. W., and Orbach, M. J. 1996. Construction and characterization of a Magnaporthe grisea bacterial artificial chromosome library. Fungal Genet. Biol. 20, 280-288. A bacterial artificial chromosome (BAC) library of Magnaporthe grisea containing 4128 clones with an average insert size of 66-kb has been constructed. This library represents seven genome equivalents of M. grisea and has been demonstrated to be representative of the genome by screening for the presence of several single-copy genes and DNA markers. The utility of the library for use in map-based cloning projects was shown by the spanning of a nine-cosmid, 207-kb DNA contig with only 3 BAC clones. In addition, using a lys1-3 auxotroph, we have shown that BAC clones at least 113 kb can be transformed into M. grisea to screen for complementation of mutations. Thus, BACs isolated in chromosome walks can be rapidly screened for the presence of the sought after gene. The ease of construction of BAC libraries and of isolation and manipulation of BAC clones makes the BAC system an ideal one for physical analyses of fungal genomes.