Factors associated with an increased risk of vertebral fracture in monoclonal gammopathies of undetermined significance

International audience

Investigating the mesh dependency and upscaling of 3D grain-based models for the simulation of brittle fracture processes in low-porosity crystalline rock

The application of 3D grain-based modelling techniques is investigated in both small and large scale 3DEC models, in order to simulate brittle fracture processes in low-porosity crystalline rock. Mesh dependency in 3D grain-based models (GBMs) is examined through a number of cases to compare Voronoi and tetrahedral grain assemblages. Various methods are used in the generation of tessellations, each with a number of issues and advantages. A number of comparative UCS test simulations capture the distinct failure mechanisms, strength profiles, and progressive damage development using various Voronoi and tetrahedral GBMs. Relative calibration requirements are outlined to generate similar macro-strength and damage profiles for all the models. The results confirmed a number of inherent model behaviors that arise due to mesh dependency. In Voronoi models, inherent tensile failure mechanisms are produced by internal wedging and rotation of Voronoi grains. This results in a combined dependence on frictional and cohesive strength. In tetrahedral models, increased kinematic freedom of grains and an abundance of straight, connected failure pathways causes a preference for shear failure. This results in an inability to develop significant normal stresses causing cohesional strength dependence. In general, Voronoi models require high relative contact tensile strength values, with lower contact stiffness and contact cohesional strength compared to tetrahedral tessellations. Upscaling of 3D GBMs is investigated for both Voronoi and tetrahedral tessellations using a case study from the AECL’s Mine-by-Experiment at the Underground Research Laboratory. An upscaled tetrahedral model was able to reasonably simulate damage development in the roof forming a notch geometry by adjusting the cohesive strength. An upscaled Voronoi model underestimated the damage development in the roof and floor, and overestimated the damage in the side-walls. This was attributed to the discretization resolution limitations.

Grip strength and functional recovery after hip fracture: An observational study in elderly population

Muscle strength is a common issue in fragility syndrome and sarcopenia, both of them involved in the pathogenesis of falls and fractures. The objective is to study the relationship between hand grip strength and functional recovery after hip fracture surgery. This prospective observational study included patients aged 65. years and older who were admitted to hospital for hip fracture surgery during a 12 month period. Functional status (Barthel Index), mental status (Cruz Roja Index), hand grip strength, 25/OH-Vitamin D plasmatic levels were evaluated at admission. Follow-up was performed 3. months after discharge to assess functional status and survival. Correlations between hand grip strength and the rest of variables were evaluated. Univariate and multivariate analyses were further applied. Mean age of subjects was 85.1. ±. 0.63 years. Out of 127 subjects, 103 were women and 24 were men. Hand grip strength was obtained in 85 patients (76.5%) and, values were between 3.3 and 24.8. kg and 81 patients (95.2%) had values below cut-point of sarcopenia considering European Working Group of Sarcopenia criteria. Hand grip strength at admission shows significant association to Barthel index at three months and functional recovery. It is also associated with age (P <. 0.001) (r = 0.81), sex (P = 0.001), cognitive status by Cruz Roja Index (P <. 0.001) and functional status measured at admission by Barthel Index (P <. 0.01) (r = -0.22). Multivariate analysis confirmed that variables were independently associated to grip strength. Hand grip strength measured at admission in Orthogeriatric Unit after hip fracture is directly related to functional recovery in elderly patients.

Impact on hip fracture mortality after the establishment of an orthogeriatric care program in a colombian hospital

El objetivo del estudio es evaluar la mortalidad a un año en pacientes con fractura de cadera, mayores de 65 años tratados en un programa establecido de orto-geriatría. 298 se trataron de acuerdo al protocolo de orto-geriatría, se calculo la mortalidad a un año, se establecieron los predictores de mortalidad orto-geriátrico. La sobrevida anual se incremento de 80% a 89% (p = .039) durante los cuatro años de seguimiento del programa y disminuyo el riesgo de mortalidad anual postoperatorio (Hazard Ratio = 0.54, p = .049). La enfermedad cardiaca y la edad maor a 85 años fueron predictores positivos para mortalidad.

Damage and fracture algorithm using the screened Poisson equation and local remeshing

We propose a crack propagation algorithm which is independent of particular constitutive laws and specific element technology. It consists of a localization limiter in the form of the screened Poisson equation with local mesh refinement. This combination allows the cap- turing of strain localization with good resolution, even in the absence of a sufficiently fine initial mesh. In addition, crack paths are implicitly defined from the localized region, cir- cumventing the need for a specific direction criterion. Observed phenomena such as mul- tiple crack growth and shielding emerge naturally from the algorithm. In contrast with alternative regularization algorithms, curved cracks are correctly represented. A staggered scheme for standard equilibrium and screened equations is used. Element subdivision is based on edge split operations using a given constitutive quantity (either damage or void fraction). To assess the robustness and accuracy of this algorithm, we use both quasi-brittle benchmarks and ductile tests.

A non-ordinary state-based peridynamics formulation for thermoplastic fracture

In this study, a three-dimensional (3D) non-ordinary state-based peridynamics (NOSB-PD) formulation for thermomechanical brittle and ductile fracture is presented. The Johnson–Cook (JC) constitutive and damage model is used to taken into account plastic hardening, thermal softening and fracture. The for- mulation is validated by considering two benchmark examples: 1) The Taylor-bar impact and 2) the Kalthoff– Winkler tests. The results show good agreements between the numerical simulations and the experimental results.

The evaluation of bone composition and carcass quality traits on back fracture in pigs stunned using electrical system.

2016

Fracture Toughening and Self-Healing of Composite Laminates by Nanofibrous Mats Interleaving

Composite laminates present important advantages compared to conventional monolithic materials, mainly because for equal stiffness and strength they have a weight up to four times lower. However, due to their ply-by-ply nature, they are susceptible to delamination, whose propagation can bring the structure to a rapid catastrophic failure. In this thesis, in order to increase the service life of composite materials, two different approaches were explored: increase the intrinsic resistance of the material or confer to them the capability of self-repair. The delamination has been hindered through interleaving the composite laminates with polymeric nanofibers, which completed the hierarchical reinforcement scale of the composite. The manufacturing process for the integration of the nanofibrous mat in the laminate was optimized, resulting in an enhancement of mode I fracture toughness up to 250%. The effect of the geometrical dimensions of the nano-reinforcement on the architecture of the micro one (UD and woven laminates) was studied on mode I and II. Moreover, different polymeric materials were employed as nanofibrous reinforcement (Nylon 66 and polyvinylidene fluoride). The nano toughening mechanism was studied by micrograph analysis of the crack path and SEM analysis of the fracture surface. The fatigue behavior to the onset of the delamination and the crack growth rate for woven laminates interleaved with Nylon 66 nanofibers was investigated. Furthermore, the impact behavior of GLARE aluminum-glass epoxy laminates, toughened with Nylon 66 nanofibers was investigated. Finally, the possibility of confer to the composite material the capability of self-repair was explored. An extrinsic self-healing-system, based on core-shell nanofibers filled with a two-component epoxy system, was developed by co-electrospinning technique. The healing potential of the nano vascular system has been proved by microscope electron observation of the healing agent release as result of the vessels rupture and the crosslinking reaction was verified by thermal analysis.

Mode-I fracture parameters of quasi-brittle materials: direct evaluation using DIC and relationship with Mode-II interfacial parameters

The objective of this thesis is the investigation of the Mode-I fracture mechanics parameters of quasi-brittle materials to shed light onto the influence of the width and size of the specimen on the fracture response of notched beams. To further the knowledge on the fracture process, 3D digital image correlation (DIC) was employed. A new method is proposed to determine experimentally the critical value of the crack opening, which is then used to determine the size of the fracture process zone (FPZ). In addition, the Mode-I fracture mechanics parameters are compared with the Mode-II interfacial properties of composites materials that feature as matrices the quasi-brittle materials studied in Mode-I conditions. To investigate the Mode II fracture parameters, single-lap direct shear tests are performed. Notched concrete beams with six cross-sections has been tested using a three-point bending (TPB) test set-up (Mode-I fracture mechanics). Two depths and three widths of the beam are considered. In addition to concrete beams, alkali-activated mortar beams (AAMs) that differ by the type and size of the aggregates have been tested using the same TPB set-up. Two dimensions of AAMs are considered. The load-deflection response obtained from DIC is compared with the load-deflection response obtained from the readings of two linear variable displacement transformers (LVDT). Load responses, peak loads, strain profiles along the ligament from DIC, fracture energy and failure modes of TPB tests are discussed. The Mode-II problem is investigated by testing steel reinforced grout (SRG) composites bonded to masonry and concrete elements under single-lap direct shear tests. Two types of anchorage systems are proposed for SRG reinforced masonry and concrete element to study their effectiveness. An indirect method is proposed to find the interfacial properties, compare them with the Mode-I fracture properties of the matrix and to model the effect of the anchorage.

Fracture toughness characterization of aluminium-epoxy adhesive joints reinforced with electrospun Nylon 6,6 nanofibers

The use of adhesives to join two different substrates is an efficient replacement to classic joining technologies such as welding and soldering. One the one hand adhesion has different advantages over those techniques such as an improved stress distribution and the potential weight reduction of the structure; on the other hand, two of the most important drawbacks are a relatively low fracture toughness and the need of an accurate surface preparation. These two aspects will be accurately analysed in the present work: the use of Nylon nanofibers as reinforcement for the adhesive should increase fracture toughness, while a surface preparation method consisting of mechanical and chemical treatments will be developed. After the specimens are produced, they will be tested in mode I fracture using a DCB (Double Beam Cantilever) test, which allows to measure the fracture toughness during crack propagation. At the end of the test, the surfaces of the adherends will be visually observed and SEM (Scanning Electronic Microscope) analysed in order to evaluate if adhesive or cohesive fracture occurred, and thus if surface treatments has been well developed to allow a better adhesive-aluminium joining.

Retrospective assessment of fracture risk through opportunistic radiological screening in a large modern cohort of liver transplant recipients

Objective: Liver transplantation has been associated with a high prevalence of osteoporosis, although most data rely on single-center studies with limited sample size, with most of them dating back to late 1990s and early 2000s. The present thesis aims to assess the prevalence of fragility fractures and contributing factors in a large modern cohort of liver transplant recipients managed in a referral Italian Liver Transplant Center. Design and Methods: Paper and electronic medical records of 429 consecutive patients receiving liver transplantation from 1/1/2010 to 31/12/2015 were reviewed, and 366 patients were selected. Clinically obtained electronic radiological images within 6 months from the date of liver transplant surgery, such as lateral views of spine X-rays or CT abdominal scans, were opportunistically reviewed in a blinded fashion to screen for morphometric vertebral fractures. Clinical fragility fractures reported in the medical records, along with information on etiology of cirrhosis and biochemistries at the time of liver surgery were also recorded. Results: Prevalence of fragility fractures in the whole cohort was 155/366 (42.3%), with no significant differences between sexes. Of patients with fractures, most sustained vertebral fractures (145/155, 93.5%), the majority of which were mild or moderate wedges. Multiple vertebral fractures were common (41.3%). Fracture rates were similar across different etiologies of cirrhosis and were also comparable in patients with diabetes or exposed to glucocorticoids. Kidney function was significantly worse in women with fractures. Independent of age, sex, alcohol use, eGFR, etiology of liver disease, lower BMI was the only independent risk factor for fractures (adjusted OR 1,058, 95%CI 1,001-1,118, P=0.046) in this study population. Conclusions: A considerable fracture burden was shown in a large and modern cohort of liver transplant recipients. Given the remarkably high prevalence of fractures, a metabolic bone disease screening should be implemented in every patient awaiting liver transplantation.

Minimal Invasive Ostheosintesis For Treatment Of Diaphiseal Transverse Humeral Shaft Fractures.

To evaluate patients with transverse fractures of the shaft of the humerus treated with indirect reduction and internal fixation with plate and screws through minimally invasive technique. Inclusion criteria were adult patients with transverse diaphyseal fractures of the humerus closed, isolated or not occurring within 15 days of the initial trauma. Exclusion criteria were patients with compound fractures. In two patients, proximal screw loosening occurred, however, the fractures consolidated in the same mean time as the rest of the series. Consolidation with up to 5 degrees of varus occurred in five cases and extension deficit was observed in the patient with olecranon fracture treated with tension band, which was not considered as a complication. There was no recurrence of infection or iatrogenic radial nerve injury. It can be concluded that minimally invasive osteosynthesis with bridge plate can be considered a safe and effective option for the treatment of transverse fractures of the humeral shaft. Level of Evidence III, Therapeutic Study.

Focal Osteoporotic Bone Marrow Defect Mimicking A Mandibular Cystic Lesion.

An unusual presentation of a focal osteoporotic bone marrow defect (FOBMD) of the mandible mimicking a cystic lesion is documented. A definitive diagnosis could be established only on the basis of the histopathologic evaluation. A 66-year-old Brazilian woman was referred by her dentist for well-defined radiolucency of the mandibular molar region suggesting a cystic lesion of odontogenic origin. The computed tomography scan confirmed that the lesion did not affect the corticals. The biopsy confirmed the diagnosis of FOBMD. The diagnostic difficulty in the current case is obvious, because FOBMD, usually exhibiting an ill-defined radiolucency, is seldom suspected preoperatively when a differential diagnosis is considered for focal well-defined radiolucent areas in the jaws.

The Influence Of Altered Occlusion On Pro-inflammatory Cytokine Levels In The Tmj Synovial Tissues Of Rats.

The aim of this study was to evaluate whether altered occlusion affects both the condylar cartilage thickness and the cytokine levels of the TMJs of rats. Thirty adult-male rats (n=30) were randomly assigned to three experimental conditions: a control group that underwent sham operations with unaltered occlusion; an FPDM group that underwent functional posterior displacement of the mandible that was induced by an incisor guiding appliance; and an iOVD group in which the increased occlusal vertical dimension was induced in the molars. The rats were subjected to the FPDM or iOVD model for 14 days and then killed. Both the right and left TMJs were removed and randomly assigned to examination with staining or immunoassay techniques. Toluidine blue staining was used to measure the thicknesses of the four layers of the articular cartilage (i.e., the fibrous, proliferating, mature, and hypertrophic layers). ELISA assays were used to assess the concentrations of the pro-inflammatory cytokines IL-1α, IL-1β, IL-6, and tumour necrosis factor (TNF-α). The measurements of the articular cartilage layers and cytokine concentrations were analyzed with ANOVA and Tukey's tests and Kruskal-Wallis and Dunn tests, respectively (α=5%). The thickness of articular cartilage in the FPDM group (0.3±0.03mm) was significantly greater than those of the control (0.2±0.01mm) and iOVD (0.25±0.03mm) groups. No significant difference was observed between the control and iOVD groups. The four articular cartilage layers were thicker in the FPDM group than in the control and iOVD groups, and the latter two groups did not differ one from each other. Both the FPDM and iOVD groups exhibited higher cytokine levels than did the control (p<0.05) group. Compared to the FPDM group, the iOVD group exhibited significantly higher levels of IL-1β and TNF-α. Both models induced inflammation in the TMJ and caused significant structural changes in the TMJ and surrounding tissues.