M. Pithioux

An alternative ultrasonic method for measuring the elastic properties of cortical bone

We studied the elastic properties of bone to analyze its mechanical behavior. The basic principles of ultrasonic methods are now well established for varying isotropic media, particularly in the field of biomedical engineering. However, little progress has been made in its application to anisotropic materials. This is largely due to the complex nature of wave propagation in these media. In the present study, the theory of elastic waves is essential because it relates the elastic moduli of a material to the velocity of propagation of these waves along arbitrary directions in a solid. Transducers are generally placed in contact with the samples which are often cubes with parallel faces that are difficult to prepare. The ultrasonic method used here is original, a rough preparation of the bone is sufficient and the sample is rotated. Moreover, to analyze heterogeneity of the structure we measure velocities in different points on the sample. The aim of the present study was to determine in vitro the anisotropic elastic properties of cortical bones. For this purpose, our method allowed measurement of longitudinal and transverse velocities (C(L) and C(T)) in longitudinal (fiber direction) and the radial directions (orthogonal to the fiber direction) of compact bones. Youngs modulus E and Poissons ratio nu, were then deduced from the velocities measured considering the compact bone as transversely isotropic or orthotropic. The results are in line with those of other methods.

Ultrasonic characterization of orthotropic elastic bovine bones

The aim of the present study was to determine the mechanical properties of bovine bones. An ultrasonic method was used to determine acoustical parameters such as the longitudinal and transverse velocities in the longitudinal and two radial directions of compact bone, i.e., in all directions of the plane. Waves propagating through bovine femoral bones were studied using an ultrasonic scanner for linear and sectorial scanning. The mechanical parameters of compact bone, such the Youngs modulus and Poissons ratio in the orthotropic case, were then determined from the measured velocities. The results are in line with those in the literature.

Femoral neck fracture prediction by anisotropic yield criteria

The fracture risk due to osteoporosis, is undertaken with Dual-Energy X-ray Absorptiometry (DEXA) which is an average of bone mineral density measurement, without taking into account the bone structure. The objective of this study was an experimental test to solicit the human proximal femurs by a physiological configuration (one leg stance phase of walking). For this, transversely isotropic finite element models were developed from CT scan acquisition. The failure load assessment was insured by anisotropic yield behaviour criteria based on distortion energy criterion (Hill’s criterion) and taking into account the difference between tension and compression yield properties (Tsai–Wu’s criterion). The results found in this study showed the significance part of anisotropic yield behaviour of bone on proximal femur.

Technical Section: ParSys: a new particle system for the introduction of on-line physical behaviour to three-dimensional synthetic objects

The incorporation of physical behaviour to synthetic objects constructed by computer is one of the main objectives of computer graphics research. In this paper we present a new interactive deformable model based on linked volumes. As such, it is straightforward and implicitly preserves the volume of the modelled objects. The proposed model resorts to Lennard-Jones potential fields for the representation of the internal energy stored in the deformable objects. Experimental results show that this new deformable model can simulate the physical behaviour of elastic volumetric objects both in a realistic and interactive way.

Optimisation of brace treatment with numerical modelling

Scoliosis is a spinal deformation which can be cured by a brace treatment. In this study, we focus on the most important group of scoliotic patients called ‘idiopathique’ (unknown origin). Most of the time, braces used the mechanical principle of three points flexion (Rigo et al. 2006). This strategy is not always efficient for stopping the spinal deformation evolution (Bullmann et al. 2004). The aim of this study is to optimise this rigid treatment. Our hypothesis is that surface loading in a specific place can correct scoliosis deformation. We can evaluate this theory by a squelettal model including disc. On one hand, it requires numerical modelling and on the other hand an exploitation by testing surface loading in order to explore new strategy.

Ultrasonic method to characterise children bone elastic properties

J.-Ph. Berteau*, P. Lasaygues, M. Pithioux and P. Chabrand Institut des Sciences du Mouvement E.J. Marey Equipe GIBO, Institute of Movement Sciences, ISM UMR 6233 CNRS/Universite de la Mediterranee, 163, Avenue de Luminy, Case Postale 918, 13288 Marseille cedex 09, France; Laboratoire de Mécanique et d’Acoustique Equipe PI, Unité Propre du CNRS UPR 7051, 31, chemin Joseph-Aiguier 13402 Marseille cedex 20, France

Adolescent idiopathic scoliosis young female rib hump: normative biomechanical data study

J.-Ph. Berteau*, Ph. Lasaygues, M. Pithioux and P. Chabrand Institut des Sciences du Mouvement E.J.Marey Equipe GIBO, Institute of Movement Sciences, ISM-UMR 6233 CNRS/Université de la Méditerranée, 163 Avenue de Luminy, Case Postale 918, 13288 Marseille Cedex 09, France; Laboratoire de Mécanique et d’Acoustique Equipe PI, Unité Propre du CNRS UPR 7051, 31, Chemin Joseph-Aiguier, 13402 Marseille Cedex 20, France

Experimental study of biomaterials for application in bone regeneration

Regeneration of large bone segments is crucial in traumatology and after tumoral bone removal. In the literature, regenerated skeletal tissue was mainly investigated for small regenerated volume (Cullinane et al. 2003; Loboa et al. 2003; Kelly and Prendergast 2005). This work aims at developing an experimental process of large volume bone regeneration. Mature skeletal tissue, such as bone, cartilage and tendon, derives from the same precursor cells: mesenchymal stem cells (Caplan 1994). Moukoko et al. (2007) develop a surgical procedure for large bone segment regeneration based on vascularised periosteal properties due to osteoprogenitor cells from its cambial layer. However, in the case of traumatisms with large bone lost, periosteum can be missing or damaged. We intend to develop a process with a biomaterial support allowing proliferation and differentiation of cultured mesenchymal cells. The choice of the biomaterials may be an important factor to determine the biological process (Barrere et al. 2008). We carried out clinical experiments to characterise the expected optimum properties of the future implant. Host tissue reaction was tested with two biomaterials: resorptive composite material (bioactiveglass and resorbable biopolymer) and tricalcium phosphate (TCP) ceramic of 80% porosity, placed at bone contact. For each material, two thicknesses, 2 and 3 mm, were compared. We studied the integration and the colonisation of the biomaterials and their resorption. These experiments aimed at answering following questions: does a membrane appear around the implant? Does a neovascularisation run in the biomaterial?

Experimental analysis of proximal femur fracture

Osteoporosis is a worldwide health problem with about 1700 fractures per day only in Europe (http://www.euro. who.int/HEN/Syntheses/osteoporosis/20060504_1). Related to age, this disease weakens the bone structure by deterioration of the trabecular architecture (Hajjar and Kamel 2004) and also decreases the cortical envelop width and increases its porosity (Bell et al. 1999). Hip fractures are the more recurrent consequences of osteoporosis, and are the cause of morbidity and increase the rate of mortality. In spite of the important incidence on the public health, its screening remains unutilized because of its cost and also, because of the technique used (DEXA). Our aim was to develop an experimental test in order to load the human proximal femurs by a physiological solicitation (one leg stance phase of walking) to retrieve the clinical osteoporosis fractures and analysis the contribution of both cortical envelop and trabecular bone in the resistance of femur structure.

Lamellar compact bone failure in tensile dynamic loading

Shock Biomechanics is a research domain mainly devoted to the development of safety conditions during locomotion and also in accidentology, or sport practices. The objective of this study is to improve the knowledge of the biomechanical behaviour of bones to sudden tensile dynamic loading. Femur and tibia are often broken during a shock, but actually, bones behaviours are studied in quasi-static but the failure caused by dynamic loading has not drawn the attention of many authors. Many of the tissues which constitute the lower limb, such as cartilage, ligaments and bones are fibrous. The objective of this work is to finely analyse the failure of a lamellar fibrous compact bone caused by a shock. The originality of this work is to describe failure in terms of the loss of cohesion between fibres of lamellar bone in dynamic loading. This model permits us to investigate the role plays by various parameters which influence failure of bones. Among them, bone porosity was found to be the most significant. In parallel, failure profiles of bovine compact bones are analysed experimentally in dynamic. Results were found to be comparable with our numerical model.