Finite Element Modeling Application in Forensic Practice: A Periprosthetic Femoral Fracture Case Study

The incidence of periprosthetic fractures has rapidly increased in the last two decades and has been the cause of a large number of revision surgeries and permanent physical disability for many patients, as well as a significant socioeconomic burden for many nations. This research deals with a periprosthetic femur fracture real event, occurred following a total hip arthroplasty and treated with one of the most widespread internal fixation methods: the implant of a periprosthetic femur plate system. A Finite Element analysis was performed to investigate the implanted femur plate break after a short follow-up and to understand the plate break causes. Such events are currently object of forensic debate as more and more often hospitals, surgeons, and medical device manufacturers are denounced by patients to whom similar events occur. In this work, different load situations acting on the femur during daily and incidental activities were simulated, in order to validate the correct behavior of the plate, according to the intended use recommended by the manufacturer. The analysis demonstrates that the plate failure can occur in situations of unconventional loading such as that caused by stumbling and in presence of incomplete bone healing

Different water and light regimes affect ionome composition in grapevine (Vitis vinifera L.)

Many inorganic cations play a major role in winemaking processes and wine quality. For this reason, chemistry at the elemental level ("ionomic") of the grape berry is of concern not only to the viticulturist, but also to the oenologist due to their direct impact on juice and must composition, which in turn affect wine quality. The aim of this research was to evaluate the effect of reduced irrigation and incident light (by means of micronized calcite) on the berry skin ionome of the Italian red grape 'Aglianico'. The study was carried out in a five-years-old vineyard (Vitis vinifera L. 'Aglianico') located in Southern Italy. Half of the plants (IRR) were drip irrigated, whereas the other half were not irrigated (NIR). Half of IRR and NIR plants were treated with Megagreen® micronized calcite. In all the treatments, plant water status and gas exchange were determined. The mean values of stem water potential (ψw) during the experiment were –1.02 and –1.10 MPa in IRR and NIR, respectively. The calcite treatments did not show changes in ψw values if compared to the untreated ones. The values of gas exchange were not statistically different among the four treatments. Grape berries were separated into three groups of mass, and the levels of macroelements, microelements and lanthanides were measured. Irrigation and calcite significantly affected macroelements distribution in all the three groups of mass, with Fe, Cu and Zn being significantly higher in the IRR and calcite-treated treatments. The effect of irrigation on the changes in microelement levels was significant for some elements. Calcite-treated vines showed higher mean values of Co, Cd, Hg and Pb. Regarding lanthanides, in calcite-untreated vines, irrigation determined significant decreases in average La, Ce, Nd, whereas in calcite-treated vines, increases in the mean concentrations of Ce, Nd, Sm, Gd, Dy, Er and Yb were found. Generally, lanthanide levels did not change between calcite-treated and untreated vines, and in all the treatments Lu resulted to be the most abundant one. Macroelements, microelements and lanthanide levels generally decreased with decreasing berry weight. The dynamics of the extractability of metals from grape berries to must during fermentation could be used to predict wine quality during the following processes and for wine traceability purposes.

On the association between helical flow and plaque progression in coronary arteries

Arterial hemodynamics is markedly characterized by the presence of helical flow (HF) patterns, whose physiological significance has been investigated in recent years, in particular with respect to the atheroprotective role played by specific HF structures. However, a gap in knowledge still exist on the significance of HF in coronary arteries, a prominent site of atherosclerotic plaque formation. The aim of this study is to carry out, in a representative sample of 15 swine coronary arteries, a systematic analysis of HF and wall thickness using computational fluid dynamics and intravascular ultrasound imaging. In detail, here we investigate possible associations of HF with (1) atherogenic wall shear stress (WSS) phenotypes, and (2) atherosclerotic plaque progression (in a follow up study). Our findings demonstrate for the first time that: (1) HF naturally characterizes coronary hemodynamics; (2) unfavourable conditions of WSS are strongly inversely associated with helicity intensity; (3) HF intensity protects against atherosclerotic plaque growth

Does the inflow velocity profile influence physiologically relevant flow patterns in computational hemodynamic models of left anterior descending coronary artery?

Patient-specific computational fluid dynamics is a powerful tool for investigating the hemodynamic risk in coronary arteries. Proper setting of flow boundary conditions in computational hemodynamic models of coronary arteries is one of the sources of uncertainty weakening the findings of in silico experiments, in consequence of the challenging task of obtaining in vivo 3D flow measurements within the clinical framework. Accordingly, in this study we evaluated the influence of assumptions on inflow velocity profile shape on coronary artery hemodynamics. To do that, (1) ten left anterior descending coronary artery (LAD) geometries were reconstructed from clinical angiography, and (2) eleven velocity profiles with realistic 3D features such as eccentricity and differently shaped (single- and double-vortex) secondary flows were generated analytically and imposed as inflow boundary conditions. Wall shear stress and helicity-based descriptors obtained prescribing the commonly used parabolic velocity profile were compared with those obtained with the other velocity profiles. Our findings indicated that the imposition of idealized velocity profiles as inflow boundary condition is acceptable as long the results of the proximal vessel segment are not considered, in LAD coronary arteries. As a pragmatic rule of thumb, a conservative estimation of the length of influence of the shape of the inflow velocity profile on LAD local hemodynamics can be given by the theoretical entrance length for cylindrical conduits in laminar flow conditions

A Eulerian method to analyze wall shear stress fixed points and manifolds in cardiovascular flows

Based upon dynamical systems theory, a fixed point of a vector field such as the wall shear stress (WSS) at the luminal surface of a vessel is a point where the vector field vanishes. Unstable/stable manifolds identify contraction/expansion regions linking fixed points. The significance of such WSS topological features lies in their strong link with “disturbed” flow features like flow stagnation, separation and reversal, deemed responsible for vascular dysfunction initiation and progression. Here, we present a Eulerian method to analyze WSS topological skeleton through the identification and classification of WSS fixed points and manifolds in complex vascular geometries. The method rests on the volume contraction theory and analyzes the WSS topological skeleton through the WSS vector field divergence and Poincare´ index. The method is here applied to computational hemodynamics models of carotid bifurcation and intracranial aneurysm. An in-depth analysis of the time dependence of the WSS topological skeleton along the cardiac cycle is provided, enriching the information obtained from cycle-average WSS. Among the main findings, it emerges that on the carotid bifurcation, instantaneous WSS fixed points co-localize with cycle-average WSS fixed points for a fraction of the cardiac cycle ranging from 0 to 14.5 % ; a persistent instantaneous WSS fixed point confined on the aneurysm dome does not co-localize with the cycle-average low-WSS region. In conclusion, the here presented approach shows the potential to speed up studies on the physiological significance of WSS topological skeleton in cardiovascular flows, ultimately increasing the chance of finding mechanistic explanations to clinical observations

Deciphering ascending thoracic aortic aneurysm hemodynamics in relation to biomechanical properties

The degeneration of the arterial wall at the basis of the ascending thoracic aortic aneurysm (ATAA) is a complex multifactorial process, which may lead to clinical complications and, ultimately, death. Individual genetic, biological or hemodynamic factors are inadequate to explain the heterogeneity of ATAA development/progression mechanisms, thus stimulating the analysis of their complex interplay. Here the disruption of the hemodynamic environment in the ATAA is investigated integrating patient-specific computational hemodynamics, CT-based in vivo estimation of local aortic stiffness and advanced fluid mechanics methods of analysis. The final aims are (1) deciphering the ATAA spatiotemporal hemodynamic complexity and its link to near-wall topological features, and (2) identifying the existing links between arterial wall degeneration and hemodynamic insult. Technically, two methodologies are applied to computational hemodynamics data, the wall shear stress (WSS) topological skeleton analysis, and the Complex Networks theory. The same analysis was extended to the healthy aorta. As main findings of the study, we report that: (1) different spatiotemporal heterogeneity characterizes the ATAA and healthy hemodynamics, that markedly reflect on their WSS topological skeleton features; (2) a link (stronger than canonical WSS-based descriptors) emerges between the variation of contraction/expansion action exerted by WSS on the endothelium along the cardiac cycle, and ATAA wall stiffness. The findings of the study suggest the use of advanced methods for a deeper understanding of the hemodynamics disruption in ATAA, and candidate WSS topological skeleton features as promising indicators of local wall degeneration

Exploring wall shear stress spatiotemporal heterogeneity in coronary arteries combining correlation-based analysis and complex networks with computational hemodynamics

Atherosclerosis at the early stage in coronary arteries has been associated with low cycle-average wall shear stress magnitude. However, parallel to the identification of an established active role for low wall shear stress in the onset/progression of the atherosclerotic disease, a weak association between lesions localization and low/oscillatory wall shear stress has been observed. In the attempt to fully identify the wall shear stress phenotype triggering early atherosclerosis in coronary arteries, this exploratory study aims at enriching the characterization of wall shear stress emerging features combining correlation-based analysis and complex networks theory with computational hemodynamics. The final goal is the characterization of the spatiotemporal and topological heterogeneity of wall shear stress waveforms along the cardiac cycle. In detail, here time-histories of wall shear stress magnitude and wall shear stress projection along the main flow direction and orthogonal to it (a measure of wall shear stress multidirectionality) are analyzed in a representative dataset of 10 left anterior descending pig coronary artery computational hemodynamics models. Among the main findings, we report that the proposed analysis quantitatively demonstrates that the model-specific inlet flow-rate shapes wall shear stress time-histories. Moreover, it emerges that a combined effect of low wall shear stress magnitude and of the shape of the wall shear stress–based descriptors time-histories could trigger atherosclerosis at its earliest stage. The findings of this work suggest for new experiments to provide a clearer determination of the wall shear stress phenotype which is at the basis of the so-called arterial hemodynamic risk hypothesis in coronary arteries