Semi-automated stereoradiographic upper limb 3D reconstructions using a combined parametric and statistical model: a preliminary study

PURPOSE: Quantitative assessment of 3D clinical indices may be crucial for elbow surgery planning. 3D parametric modeling from bi-planar radiographs was successfully proposed for spine and lower limb clinical investigation as an alternative for CT-scan. The aim of this study was to adapt this method to the upper limb with a preliminary validation. METHODS: CT-scan 3D models of humerus, radius and ulna were obtained from 20 cadaveric upper limbs and yielded parametric models made of geometric primitives. Primitives were defined by descriptor parameters (diameters, angles...) and correlations between these descriptors were found. Using these correlations, a semi-automated reconstruction method of humerus using bi-planar radiographs was achieved: a 3D personalized parametric model was built, from which clinical parameters were computed [orientation and projections on bone surface of trochlea sulcus to capitulum (CTS) axis, trochlea sulcus anterior offset and width of distal humeral epiphysis]. This method was evaluated by accuracy compared to CT-scan and reproducibility. RESULTS: Points-to-surface mean distance was 0.9 mm (2 RMS = 2.5 mm). For clinical parameters, mean differences were 0.4-1.9 mm and from 1.7° to 2.3°. All parameters except from angle formed by CTS axis and bi-epicondylar axis in transverse plane were reproducible. Reconstruction time was about 5 min. CONCLUSIONS: The presented method provides access to morphological upper limb parameters with very low level of radiation. Preliminary in vitro validation for humerus showed that it is fast and accurate enough to be used in clinical daily practice as an alternative to CT-scan for total elbow arthroplasty pre operative evaluation

Nonlinear ultrasound monitoring of fatigue microdamage accumulation in cortical bone

Accumulation of bone micro-damage is suspected to lead to severe impairment of mechanical properties with an increase in skeletal fragility and fracture risk. The objective of the study was to evaluate the potential of Nonlinear Resonant Ultrasound Spectroscopy (NRUS) for measuring micro-damage accumulation in cortical bone using four-point bending cycling fatigue. Sixteen human cortical bone specimens were machined as parallelepiped beams. Damage progression was controlled by measuring the linear elastic beam theory modulus (E LEBT ), known to reflect microdamage accumulation. Before and between each damage step, the nonlinear ultrasonic elastic coefficient was measured by NRUS. At the end of each cycling fatigue, a subset of bone samples was measured by μCT at the European Synchrotron Radiation Facility. Results showing a progressive increase of nonlinear ultrasonic elastic coefficient along fatigue cycling suggest that NRUS measurements are sensitive to micro-damage accumulation. The results mentioned above were validated using synchrotron radiation μCT. The variation of elastic nonlinearity was found to be significantly correlated to the variation of number density of small microcracks which almost doubled in damaged regionsThis research was supported by the Agence Nationale pour la Recherche (ANR), France (Grant BONUS_07BLAN0197

Multiaxial experiments with radial loading paths on a polymeric foam

Cellular materials such as polymeric foams in particular have been widely studied under uniaxial loading conditions. Many experimental studies have been focusing recently, however, on the responses of these foams to multiaxial loads. In the present study, a novel experimental hexapod device was used to perform combined uniaxial compression and simple shear tests. Using a post-processing method of analysis which can be used to study elementary mechanical behavior, the authors show the occurrence of non-proportional stress paths in the material under investigation although proportional kinematic paths were imposed. A failure limit criterion is presented for use with the foam of interest. The results of the present analysis yield useful information for meeting our future objective, namely to develop a numerical model for simulating multiaxial loading conditions.FUI GENOSI

Effect of block copolymer nano-reinforcements on the low velocity impact response of sandwich structures

Sandwich composites with fibre reinforced plastic (FRP) facesheets have emerged as a major class of lightweight structural materials in a wide range of engineering fields including aerospace, automotive and marine structures. This is due to attractive mechanical properties such as high specific stiffness and high strength. However, sandwich structures are susceptible to damage caused by impact. The objective of this paper is to evaluate the dynamic response of sandwich composites based on Kevlar fibre reinforced epoxy and Rohacell foam. The improvement in impact performance of these sandwich structures that can be achieved by the addition of nanoparticles in the resin matrix is investigated. Nanostrength, an acrylate triblock copolymer that self-assembles in the nanometer scale is added to the epoxy matrix. The effect of the nano-reinforcements on flat sandwich plates under low velocity impact is investigated at different scales. An instrumented drop tower setup is used for the low velocity impact tests of the sandwich plates with neat or nano-reinforced epoxy matrix, at different energies. The macroscopic response of the sandwich structure and the microscopic phenomena involved in dissipating the impact energy are identified and compared for sandwich plates with and without nanoparticles

Monitoring trabecular bone microdamage using a dynamic acousto-elastic testing method

Dynamic acousto-elastic testing (DAET) is based on the coupling of a lowfrequency (LF) acoustic wave and high-frequency ultrasound (US) pulses (probing wave). It was developed to measure US viscoelastic and dissipative non-linearity in trabecular bone. It is well known that this complex biphasic medium contains microdamage, even when tissues are healthy. The purpose of the present study was to assess the sensitivity of DAET to monitor microdamage in human calcanei. Three protocols were therefore performed to investigate the regional heterogeneity of the calcaneus, the correlation between DAET measurements and microdamage revealed by histology, and DAET sensitivity to mechanically induced fatigue microdamage. The non-linear elastic parameter b was computed for all these protocols. The study demonstrated the presence of high viscoelastic and dissipative non-linearity only in the region of the calcaneus close to the anterior talocalcaneal articulation (region of high bone density). Protocols 1 and 2 also showed that most unsorted calcanei did not naturally exhibit high non-linearity, which is correlated with a low level of microcracks. Nevertheless, when microdamage was actually present, high levels of US non-linearity were always found, with characteristic non-linear signatures such as hysteresis and tension/compression asymmetry. Finally, protocol 3 demonstrated the high sensitivity of DAET measurement to fatigue-induced microdamage.Agence Nationale pour la Recherche (ANR), France [Grant BONUS_07BLAN0197]

Influence of heterogeneities on mechanical properties: Virtual material concept

The present article is connected to the study of a bituminous mixture (BM) material, used on modern railway track as sub-ballast layer. Influence of size and volume fraction of rigid monodisperse spherical inclusions, randomly packed into a hyperelastic matrix, on the mechanical behavior of an obtained composite structure was investigated using ‘‘Virtual Material” approach. 3D geometry of inclusions was defined and used for 3D printing and 3D finite element modeling. This approach allows a numerical study of a theoretical case without losing connection with real experiment (by means of direct geometrical correspondence). Parameters of 7 specimens were chosen in accordance with a Doehlert experimental design. Analysis performed on the basis of the ‘‘response surfaces” approach has shown that mechanical parameters of studied specimens have a strong dependence on the value of inclusions volume fraction and almost no dependence on the value of the size of inclusions. Stress/strain concentrations were analyzed using FE method in order to find and to visualize load-bearing chains going through the matrix. It was found that Von Mises stress in load-bearing chains is almost 8 times higher than the average in the matrix

Strain rate influence on mechanical behavior of a single wire entangled material

In a global context of energy saving, the ratio stiffness – mass is a key parameter for design of mechanical structures. To deal with this major concern, sandwich materials are finding an increasing use: the skins are designed to resist tensile and compressive stresses while the core needs to gather lightweight, shear stresses resistance and high mechanical energy absorption capacities. Firstly made of balsa wood, the core is nowadays classically realized using architectured materials (cellular materials, honeycombs, entangled materials, etc.). Entangled materials are architectured materials with tuneable properties, depending of the dedicated application. Several entangled materials already exist such as mineral or metallic wool; some of them are made of a single ductile metallic wire, entangled in all directions so that the final material becomes a porous continuous media. Such materials, which combine lightness and ductile behaviour, seem to be perfect candidates to dissipate energy during an impact. Compared to conventional materials such as balsa wood or honeycomb, a large amount of energy is indeed dissipated by friction coming from the numerous contacts due to the entanglement. The global aim of this work is focused on the study of energy dissipation mechanisms involved during impact as well as the correlation between architectural parameters of the material (wire diameter and material, volume fraction, etc.) and macroscopic behaviour. The first step that is presented here consists of an experimental investigation using dynamic compression tests to study macroscopic parameters (wire diameter, volume fraction, etc.) on absorbed energy

Biomechanics of surfing: development and validation of an instrumented surfboard to measure surfboard kinetics

The purpose of this study was to investigate the different relations between the actions of a surfer and the kinematic behaviour of his surfboard. An instrumented surfboard has been designed with a force platform synchronized with an inertial measurement unit and acquisition system. An experimental campaign has been carried out in situ, where different waves have been surfed to validate the device. Results revealed that measured efforts of the surfer and kinematics of his surfboard are consistent regarding the expected behaviour. Instrumented surfboards will help coaches by giving them a new performance analysis tool. It will also provide an experimental database for the development of numerical models about interactions Surfer/Surfboard/Wave

System Identification using in situ experimental data for the development of a Hexapod Surfing Simulator

International audienc

Volley-ball : contrôler la réception en direction et en intensité

Pour que les élèves progressent en réception, l'enseignant les aide à construire 'le point mort haut' de la trajectoire de balle, en insistant sur la nécessité de donner un temps d'organisation motrice à ses partenaire