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CONTENTS
Volume 1, Number 3, September 2014
 

Abstract
Forearm fractures in children are very common among all pediatric fractures. However, biomechanical investigations on the pediatric forearm are rather scarce, partially due to the complex anatomy, closely situated, interrelated structures, highly dynamic movement patterns, and lack of appropriate tools. The purpose of this study is to develop a computational tool for child forearm investigation and characterize the mechanical responses of a backward fall using the computational model. A three-dimensional ten-year-old child forearm finite element (FE) model, which includes the ulna, radius, carpal bones, metacarpals, phalanges, cartilages and ligaments, was developed. The high-quality hexahedral FE meshes were created using a multi-block approach to ensure computational accuracy. The material properties of the FE model were obtained by scaling reported adult experimental data. The design of computational experiments was performed to investigate material sensitivity and the effects of relevant parameters in backward fall. Numerical results provided a spectrum of child forearm responses with various effective masses and forearm angles. In addition, a conceptual L-shape wrist guard design was simulated and found to be able to reduce child distal radius fracture.

Key Words
pediatric forearm fractures; finite element model; pediatric biomechanics; parametric study; wrist guard design

Address
Department of Biomedical Engineering, Wayne State University

Abstract
The aim of this study was to evaluate the influence of disc thickness on the normal behavior of the temporomandibular joint. Based on a specific patient case, CT scan images showing accentuated wear in the right disc were reconstructed and the geometrical and finite element model of the temporomandibular joint structures (cranium, mandible, articular cartilages and articular discs) was developed. The loads applied in this study were referent to the five most relevant muscular forces acting on the temporomandibular joint during daily tasks such as talking or eating. We observed that the left side structures of the temporomandibular joint (cranium, mandible and articular disc) were the most affected as a consequence of the wear on the opposite articular disc (right side). From these results, it was possible to evaluate the differences in the two sides of the joint and understand how a damaged articular disc influences the behavior of this joint and the possible consequences that can arise without treatment.

Key Words
Articular disc wear; finite element models; muscular forces; numerical analysis; temporomandibular joint

Address
Ricardo J. Duarte and Antonio Ramos: DTEMA, Department of Mechanical Engineering, University of Aveiro, 3810-197 Aveiro, Portugal
Ricardo J. Duarte and Michel Mesnard: Universite de Bordeaux, Institut de Mecanique et d

Abstract
Computational multibody models of the elbow can provide a versatile tool to study joint mechanics, cartilage loading, ligament function and the effects of joint trauma and orthopaedic repair. An efficiently developed computational model can assist surgeons and other investigators in the design and evaluation of treatments for elbow injuries, and contribute to improvements in patient care. The purpose of this study was to develop an anatomically correct elbow joint model and validate the model against experimental data. The elbow model was constrained by multiple bundles of non-linear ligaments, three-dimensional deformable contacts between articulating geometries, and applied external loads. The developed anatomical computational models of the joint can then be incorporated into neuro-musculoskeletal models within a multibody framework. In the approach presented here, volume images of two cadaver elbows were generated by computed tomography (CT) and one elbow by magnetic resonance imaging (MRI) to construct the three-dimensional bone geometries for the model. The ligaments and triceps tendon were represented with non-linear spring-damper elements as a function of stiffness, ligament length and ligament zero-load length. Articular cartilage was represented as uniform thickness solids that allowed prediction of compliant contact forces. As a final step, the subject specific model was validated by comparing predicted kinematics and triceps tendon forces to experimentally obtained data of the identically loaded cadaver elbow. The maximum root mean square (RMS) error between the predicted and measured kinematics during the complete testing cycle was 4.9 mm medial-lateral translational of the radius relative to the humerus (for Specimen 2 in this study) and 5.30 internal-external rotation of the radius relative to the humerus (for Specimen 3 in this study). The maximum RMS error for triceps tendon force was 7.6 N (for Specimen 3).

Key Words
elbow; biomechanics; multibody; ligament; cartilage

Address
Munsur Rahman, Yunkai Lu and Trent M. Guess: Department of Civil and Mechanical Engineering, University of Missouri-Kansas City, 5110 Rockhill Road, Kansas City, MO 64110, USA
Akin Cil, Michael Johnson and Trent M. Guess: Department of Orthopaedic Surgery, University of Missouri-Kansas City, 2411 Holmes Street, Kansas City, MO 64108, USA
Akin Cil and Michael Johnson: Department of Orthopaedics, Truman Medical Centers, 2301 Holmes Street, Kansas City, MO 64108, USA


Abstract
With the goal of increasing the survivorship of the prosthesis and anticipating primary stability problems of new prosthetic implants, finite element evaluation of the micromotion, at an early stage of the development, is mandatory. This allows assessing and optimizing different designs without manufacturing prostheses. This study aimed at investigating, using FEA, the difference in the prediction of the primary stability of cementless hip prostheses implanted into a Sawbones

Key Words
total hip arthroplasty; cementless stem; primary stability; material properties; finite element analysis

Address
Department of Laboratoire de recherche en imagerie et orthopedie, Departement de genie de la production automatisee, Ecole de technologie superieure 1100 rue Notre-Dame Ouest, Montreal, Quebec, H3C 1K3, Canada,

Abstract
The usual assumption that the increase of fractures in aging bone is due entirely to lower bone density is taken back with respect to the possibility that aging bone fractures result from a loss of stability, or buckling, in the structure of the bone lattice. Buckling is an instability mode that becomes likely in end-loaded structures when they become too slender and lose lateral support. The relative importance of bone density and architecture in etiology bone fractures are poorly understood and the need for improved mechanistic understanding of bone failure is at the core of important clinical problems such as osteoporosis, as well as basic biological issues such as bone formation and adaptation. These observations motivated the present work in which simplified adaptive-beam buckling model is formulated within the context of the adaptive elasticity (Cowin and Hegedus, 1976; Hegedus and Cowin, 1976). Our results indicate that bone loss activation process leads systematically to the apparition of new elastic instabilities that can conduct to bone-buckling mechanism of fracture.

Key Words
Adaptive elasticity; bone remodeling; beam buckling theory

Address
Salah Ramtani: Laboratoire CSPBAT – LBPS UMR 7244 CNRS, Universite Paris-Nord,Institut Galilee 99, avenue J.B. Clement. 93430 Villetaneuse, France
Hamza Bennaceur and Toufik Outtas: Laboratoire Mecanique des Structures et Materiaux, Universite de Batna,Departement de Mecanique, Faculte de technologie, Avenue Chahid Boukhlouf 05000, Batna, Algerie


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