Technology and Health Care - Volume 14, issue 4-5

Article Type: Editorial

DOI: 10.3233/THC-2006-144-501

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 199-200, 2006

Authors: Ohrndorf, A. | Krupp, U. | Christ, H.-J.

Article Type: Research Article

Abstract: The aim of this paper is to report on the characterization of the influences of foam homogeneity and the cell strut material on the mechanical behaviour and the fracture mode of metallic foams that are promising candidates for new perfectly tailored medical implants. For two open-cell foams with identical cell geometries produced in the same precision-casting process but using different cell strut materials, the stress-strain behaviour and the evolution of damage until fracture is compared. To account for effects arising from a change in the geometry of the cell structure and the resulting homogeneity of the foam, the main characteristics …of fracture for the group of closed-cell foams were included in this study. Monotonic tests carried out in compression revealed that foam homogeneity is the major factor with respect to the formation of deformation bands prior to cell collapse in metallic foams. The influence of the cell strut ductility is particularly pronounced in monotonic tension where the fracture mode changes from extremely brittle fracture to strongly plastically deformed cells, with substantial fracture elongation. In tension-tension fatigue as well as under symmetric push-pull loading conditions, damage is governed by a combination of cyclic creep and fatigue crack propagation through the specimen. From a mechanistic point of view no fundamental differences between the three foams tested were detected for these loading conditions. However, in compression-compression fatigue the same dependencies in terms of homogeneity and ductility influence the mechanisms of strain evolution that are active in monotonic compression. Show more

DOI: 10.3233/THC-2006-144-502

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 201-208, 2006

Authors: Liepsch, Dieter

Article Type: Research Article

Abstract: Biofluid mechanics is a complex field that focuses on blood flow and the circulation. Clinical applications include bypass and anastomosis surgery, and the development of artificial heart valves and vessels, stents, vein and dialysis shunts. Biofluid mechanics is also involved in diagnostic and therapeutic measures, including CT and MRI, and ultrasound. The study of biofluid mechanics involves measuring blood flow, pressure, pulse wave, velocity distribution, the elasticity of the vessel wall, the flow behavior of blood to minimize complications in vessel,- neuro-, and heart surgery. Biofluid mechanics influence the lungs and circulatory system, the blood flow and micro-circulation; lymph flow, …and artificial organs. Flow studies in arterial models can be done without invasive techniques on patients or animals. The results of fluid mechanic studies have shown that in the addition to basic biology, an understanding of the forces and movement on the cells is essential. Because biofluid mechanics allows for the detection of the smallest flow changes, it has an enormous potential for future cell research. Some of these will be discussed. Show more

DOI: 10.3233/THC-2006-144-503

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 209-214, 2006

Authors: Vejpustková, J. | Vilímek, M. | Sochor, M.

Article Type: Research Article

Abstract: Today artificial neural networks can be trained to solve problems that are difficult for conventional computers or human beings. The big advantage of an artificial neural network is results obtained without knowledge of the algorithm procedure or without full and exact information. Therefore an artificial neural network was used to predict the muscle forces. The aim of the study was to simplify prediction of muscle forces which are difficult to determine, because many muscles act cooperatively. However, orthopeadists, biomechanical engineers and physical therapists need to take muscle forces into consideration because joint contact forces, as well as muscle forces, need …to be estimated in order to understand the joint and bone loading. In terms of sensitivity of the muscle parameters to the results from the proposed neural network object, the muscle force prediction was simplified. Show more

DOI: 10.3233/THC-2006-144-504

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 215-218, 2006

Authors: Goldmann, Tomáš | Seiner, Hanuš | Landa, Michal

Article Type: Research Article

Abstract: Elastic properties of single parts of a human skeleton are necessary to know for modelling bone tisue-implants interactions as well as for diagnostic purposes. This paper contributes to the methodology of the evaluation of elastic properties of bones by the ultrasonic wave inversion. The method was developed on composite structures such as plates and cylindrical shells. Final results are then demonstrated on the bovine cortical bone specimen. Properties are supposed to exhibit an orthotropic or a transversally isotropic symmetry. Quasi-longitudinal and quasi-transversal waves are generated from the wave diffraction on the liquid/specimen interface. Wave velocity fields obtained by …the ultrasonic scanning technique are used as an input to the inversion procedure for all elastic constants determination. Experimental results are confronted with the numerical modelling of the wave propagation and the stability of resulting data is evaluated by the statistical method based on the Monte-Carlo simulation. The suggested approach has a potential for the qualify of such measurements performed on fresh bones and also for improvement in-situ ultrasonic techniques. Show more

DOI: 10.3233/THC-2006-144-505

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 219-232, 2006

Authors: De Beule, M. | Van Impe, R. | Verhegghe, B. | Segers, P. | Verdonck, P.

Article Type: Research Article

Abstract: In Western countries, cardiovascular disease is the most common cause of death, often related to atherosclerosis. This paper offers a brief introduction into some aspects of this disease and its treatment, where the use of stents is gaining increasing importance. Stents are supporting – mostly metal – tubular mesh structures which are opened in an obstructed artery in order to reopen it, and to offer radial strength to prevent elastic recoil of the dilated vessel. In addition to a variety of experimental tests to study the behavior of (new) stent designs, advanced numerical models (e.g. Finite Element Models) may offer …interesting insights in the mechanical behavior of stents and will undoubtedly influence the design of future generation stents. A brief literature review on numerical studies dealing with the mechanical behavior of stents is presented. Subsequently, the finite element method is exploited to investigate and compare different designs of a “first generation” Palmaz Schatz stent in order to reduce the dogboning (i.e. ends of stent open first during expansion) to a minimum. Our computational models (Abaqus [1]) are described in terms of geometry, constitutive material models, numerical aspects and output quantities. Altering the original symmetric stent design to asymmetric designs decreased the dogboning from 27.24% to less than 10% for the vast majority of the studied asymmetric designs. For one particular configuration, the dogboning effect vanished completely. For this reason, taking asymmetry into account in the design of stents seems very promising, at least from the perspective of dogboning. However, as the dogboning only takes into account the radii (R) at the central and distal part of the stent, nothing can be concluded concerning the uniformity of the complete stent expansion. The mean value (Rm ) and the root mean square (RRMS ) of radii (differences) of the stent at the end of the loading phase (P=0.7 N/mm2 ) are much better parameters to give a clear indication of the uniformity of the expanded stent's shape. Although the model is suitable to study basic aspects of stent deployment, further research is necessary, especially accounting for newer generation stent geometries and more realistic balloon-stent interaction. Show more

DOI: 10.3233/THC-2006-144-506

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 233-241, 2006

Authors: Zsidai, Attila | Kocsis, László

Article Type: Research Article

Abstract: A modern motion analysis laboratory was installed by way of several scientific research instrumentation grants awarded to the Department of Applied Mechanics, BUTE. Motion and spine analysis is performed by a CMS-HS ultrasound-based system. System operation is based on ultrasound spread characteristics. In the area of spine analysis, it is possible to investigate the shape of the spine, its movement characteristics, mobility, and the movement characteristics of the cervical spine separately. The results of traditional spine tests are adequately supplemented by the results of the tests performed by this motion analysis system, considered to be a specialty throughout Europe. With …the EMG (ElectroMyoGraph) sensors specify whether the muscles operate insufficiently or become active during the wrong motion, limiting the patient in motion. Show more

DOI: 10.3233/THC-2006-144-507

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 243-250, 2006

Authors: Paróczai, Róbert | Kocsis, László

Article Type: Research Article

Abstract: Recently, there has been great improvement in the field of movement analysis, which is a worldwide tendency. There is a continuous improvement of new methods, combined with traditional ones. In the last few years, we have managed to set up a modern, absolutely up-to-date motion analysis laboratory at the Budapest University of Technology and Economics (BUTE). The primary purpose of this study was to determine usual walking and running parameters as a function of speed and compare our results with the data of other studies. We tested the gait and running characteristics of people at different speeds, measuring …the usual parameters of walking and running. On the basis of these measurements, we observed the interrelation of the three main parameters of gait and running (speed, cadence, stride length) and determined the dependence of cadence and stride length on speed as well. The determined energetically optimal walking speed (EOWS) and the usual walking speed (UWS) correlate well with the values in literature. Our measurements were performed on a running corridor, and at the facilities provided by the Biomechanical Laboratory, including an instrumented treadmill connected to the measurement system. Show more

Keywords: Gait analysis, running analysis, kinematic and kinetic parameters, speed

DOI: 10.3233/THC-2006-144-508

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 251-260, 2006

Authors: Füchtmeier, B. | May, R. | Fierlbeck, J. | Hammer, J. | Nerlich, M.

Article Type: Research Article

Abstract: A new humerus nail (Sirus™) has become available for the treatment of fractures of the proximal humerus. The aim of the study was the biomechanical comparison of this implant with established systems. 12 matched pairs of human humeri were employed for testing. Three randomized groups were formed (n=4 pairs). A bending moment of 7.5 Nm and a torsional moment of 8.3 Nm were applied in a test of five loading cycles to all intact bones. Loading was consistently initiated at the distal epiphysis. The consequent deformation at the distal epiphysis was continuously recorded. Then an osteotomy with a …defect of 5 mm was created to simulate an unstable subcapital humerus fracture. For paired comparison, one of each pair was stabilized with the Sirus proximal humerus nail. The other side was fixed with a reference implant. The following groups were created.: Group I: Sirus versus Proximal humerus nail (PHN) with spiral blade. Group II: Sirus versus PHILOS plate. Group III: Sirus versus 4.5 mm AO T-plate. The proximal humerus nail (Sirus) demonstrated significantly higher stiffness values than the reference implants for both bending and torsional load. The following values were recorded at a bending moment of 7.5 Nm: Sirus 14.2 mm, PHN 20.7 mm, PHILOS plate 28.1 mm, 4.5 AO T-plate 29.3 mm p<0.0012). The values at 8.3 Nm torsional moment were: Sirus 8.5°, PHN 12.3°, PHILOS plate 16.4°, 4.5 AO T-Platte 15.6° (p<0.002). The intramedullary load carriers were biomechanically superior when compared to the plating systems in the fracture model presented here. Supplementary, the Sirus Nail showed higher stiffness values than the PHN. However, the latter are gaining in importance due to the possibility of minimal invasive implantation. Whether this will be associated with functional advantages requires further clinical investigation. Show more

Keywords: Proximal humerus fractures, biomechanical analysis, Sirus nail

DOI: 10.3233/THC-2006-144-509

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 261-270, 2006

Authors: Vaverka, Michal | Návrat, Tomáš | Vrbka, Martin | Florian, Zdeněk | Fuis, Vladimír

Article Type: Research Article

Abstract: Many disorders of the hip can be treated with a suitable osteotomy based on the improvement of mechanical conditions in the hip joint. These operations, such as osteotomies are very complex. The surface replacement has also been developed as an alternative to a total hip replacement for young and more active people. It is up-to-date to concern with biomechanics of pathological hips and it is necessary to supplement the existing clinical findings with the results of mechanical analyses. Several finite element (FE) models are presented in this paper. The first one offers solutions to the strain-stress analysis of the physiological …hip. The second one represents dysplastic hip joint. Another two computational models of both hips of a young patient were created (FE model of physiological hip and pathological hip affected by Perthes disease with a deformed shape of the femoral head). Also a computational model is presented, which enables us to investigate strain and stress parameters in the hip joint with applied surface replacement. The strain and stress analysis was performed by means of finite element method (FEM) in ANSYS system. Show more

DOI: 10.3233/THC-2006-144-510

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 271-279, 2006

Authors: Yang, T.H.J. | Leung, S.K.W. | Phipps, S. | Reuben, R.L. | McNeill, S.A. | Habib, F.K. | Schnieder, A. | Stevens, R.

Article Type: Research Article

Abstract: In vitro macro- and micro-indentation test systems have been designed to measure the dynamic micro-mechanical properties of human prostate tissues at actuation frequencies between 5 Hz and 30 Hz, and 0.5 Hz and 20 Hz, respectively. The development of in vitro test systems was aimed at assessing the capacity of such an in vivo medical probe to provide information useful for the diagnosis of various prostate diseases. The macro-indentation test system is an established one, which we have used to determine structure-property relationships in human and canine prostate tissues and here we use it to validate a newly-developed …micro-indentation test system using a tissue phantom. Mechanical testing was also carried out on sections of prostate tissue harvested from cystectomy and radical prostatectomy, diagnosed with bladder cancer and benign prostatic hyperplasia. Dynamic probing under displacement control was carried at pre-strains between 5% and 8% for macro-probing and at 5% pre-strain for micro-probing, and the general effect of pre-strain on the dynamic mechanical properties (described by the amplitude ratio between stress and strain, and the phase lag between strain and stress) of phantom and prostate tissues is presented. Specific point probing on epithelial and stromal histological components was also carried out showing a significant difference between the amplitude ratios of epithelial and stromal components for actuation frequencies exceeding 5 Hz. However, no significant difference was found between phase lags for epithelial and stromal tissues. Show more

Keywords: Dynamic modulus, soft tissue biomechanics, BPH, prostate

DOI: 10.3233/THC-2006-144-511

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 281-296, 2006

Authors: Lakshmanan, V. | Yang, T.H.J. | Reuben, R.L. | Hammer, J. | Else, R.W.

Article Type: Research Article

Abstract: The overall aim of this study is to establish relationships between the histology of biological tissues and their mechanical properties, especially their dynamic modulus. The emphasis is on the physical scale of the probe used in relation to the size of the histological features in the material of interest. The selection of a model system (connective tissue) is described along with a corresponding gelatin-based system in which the make-up of the material can be “engineered” reproducibly. Next three experimental rigs are described with regard to their suitability for making measurements at a variety of scales; the micro-scale, the …meso-scale and the macro-scale. Finally, some preliminary measurements on the micro-scale rig are presented and preliminary conclusions drawn on the methodology. Show more

Keywords: AFM, tissue-mimic, structure-property relationships, biological materials

DOI: 10.3233/THC-2006-144-512

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 297-309, 2006

Authors: Bursa, Jiri | Lebis, Radek | Janicek, Premysl

Article Type: Research Article

Abstract: The paper deals with problems related to computational modelling of stress-strain states in vascular smooth muscle cells (SMCs). First, motivation for stress-strain analysis of SMCs is presented. Problems of their structure, geometry, constitutive models and initial (stress-free) state are analyzed on the basis of anatomical, histological and physiological knowledge. Various types of computational FE models of SMCs are presented; their constitutive models are identified on the basis of published mechanical tests carried out with SMCs cultured in vitro. Results of two models are presented; the former is a homogeneous model of the cell tension test with hyperelastic constitutive relations of …the cell material. The latter model is more complex, it comprehends cortical and deep cytoskeleton, modelled as a tensegrity structure, and homogeneous linear elastic nucleus and remaining cytoplasm; it is used in computational modelling of indentation test. Perspectives, assumptions and limitations of computational modelling of SMCs under physiological load are discussed. Show more

DOI: 10.3233/THC-2006-144-513

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 311-320, 2006

Authors: Glinkowski, Wojciech | Górecki, Andrzej

Article Type: Research Article

Abstract: Introduction: The use of noninvasive, acoustic methods like ultrasonometry is becoming increasingly interesting in the quantitative assessment of fracture healing. A reliable measurement technique has been described using ultrasonic transducers placed across the fracture gap. Ultrasonic image aiming is useful for accurate transducers location, on both sides of the gap. The study was designed to assess the clinical application of measurement of ultrasonic wave propagation through the fracture callus. Material and Methods: Contact testing was performed with a prototype ultrasonic bone tester UTTK-01 device. The measuring technique was validated experimentally on human long bones in vitro, as well …on volunteers. Twenty four diaphyseal fractures of long bones were prospectively assessed. Transducers put on a fixed distance frame were properly placed with ultrasonographic focusing. Results: Average ultrasound propagation time was 1917 m/s. The measured values for fractures rose with time after injury. The average speed of sound measured between 10th and 21st day after fracture was 1200,85 m/s, after 7 to 8 weeks – 1559,35 m/s, after 12 weeks – 1640,64 m/s, after 16 weeks – 1735,72 m/s. Conclusions: We conclude that the technique for measuring long bone ultrasound velocity with ultrasonographic centering on the fracture gap allows repetitive positioning of ultrasonic transducers for measurement. Ultrasonic measurement of bone union may support or modify clinical decision. However, further studies are required to make the ultrasonometric method easier and more user friendly for clinical studies. Show more

Keywords: Fracture healing, assessment, monitoring, cortical bone, quantitative ultrasound, ultrasonometry

DOI: 10.3233/THC-2006-144-514

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 321-333, 2006

Authors: Blythe, A. | Tasker, T. | Zioupos, P.

Article Type: Research Article

Abstract: The performance of ACL grafts in both the short and long term is only as good as the condition of the graft at the time of surgery. If the graft lengthens under load at the two fixation ends incorporation will take longer to occur. Previous studies have shown that the various grafts currently used are strong enough. However, data on strength came primarily from quasistatic single pull to failure tests with, in some cases, modest cycling to precondition the grafts. The present study examined the in-vitro biomechanical behaviour of model ACL grafts, which have been fatigue cycled to failure over …a wide range of loads in physiological ambient conditions. Load/deformation curves and the stretch of the grafts was continuously recorded until final rupture. The grafts demonstrated typical creep-rupture like behaviour with elongation (non-recoverable stretch) and loss of stiffness leading to gradual failure. Some of the graft designs were consistently shown to elongate up to 20 mm in length within the first 2000 cycles at moderate physiological loads and a further 10 mm of elongation occurred between the initial preconditioned state and just prior to complete rupture. Not enough attention has been paid previously to the likely long term elongation patterns of ACL grafts post-surgery and even after the usual empirical preconditioning has been performed by the surgeon. Increased graft dimensions may result in recurrent knee instability and may also lead to failure of the graft to incorporate. Preconditioning in-vitro may still be a way to remove some slack and prepare the graft for its operational environment by stiffening in particular the tissue/fixation interface for those grafts that use soft polymer fixation ends. Show more

Keywords: ACL grafts, in-vitro biomechanical performance, (pre)conditioning, elongation, laxity

DOI: 10.3233/THC-2006-144-515

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 335-347, 2006

Authors: Mefti, Nacim | Ganghoffer, Jean François | Haussy, Bernard

Article Type: Research Article

Abstract: Cell adhesion plays an important role in biology: essentially with regard to immunizing defence and the transport of medicinal substances toward specific zones. The focus is here on the mechanical description of adhesion kinetics, in terms of the failure and creation of connections during the rolling phenomenon. Hence, we consider the case of a single cell, which is linked to a rigid substratum. A 2D model is established. We consider that the contact zone cell-wall is rectilinear and composed of vertical fibers and two horizontal rigid beams (complex cell membrane- fibers-vein wall). These connections are modeled by elastic …springs having identical elastic properties (e.g stiffness), but different failure strengths. The cell is subjected to the flow of plasma, which can generate the rolling phenomenon; we accordingly consider two distinct zones, one associated with the failure of the old fibers and one with the creation of the new fibers (in the direction opposite to the flow). Several interactions are taken into account in this model: van der Waals (attractive) and electrostatic (repulsive) forces and the effects of fluid pressure, assimilated into a periodic point force applied to the interface zone. We also study the vibration induced failure in the contact zone without mechanical damping using the principle of virtual work and a failure criterion to establish the equation of motion and the time evolution of the failure (dynamical approach). Rupture of a fiber can occur if the stress applied to the fiber is above a certain limit. These limits are determinated with using a probabilistic approach by use of a spectral method to simulate a stochastic and Gaussian field. Modeling of the creation of new fibers is also achieved by the combination of a dynamical and probabilistic method and a kinematical criterion. On the basis of these elements, numerical simulations are developed, that elucidate the rupture and rolling phenomena. Show more

Keywords: Cel, adhesion, failure, probabilistic description, fiber, time dependence

DOI: 10.3233/THC-2006-144-516

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 349-358, 2006

Authors: Lee, T.C. | O'Brien, F.J. | Gunnlaugsson, T. | Parkesh, R. | Taylor, D.

Article Type: Research Article

Abstract: Mechanobiology is concerned with the relationships between mechanical forces and biological processes. Bone adapts to altered mechanical loading by modelling and remodelling. Microdamage is a stimulus for adaptation as shown by a sheep overload model. If microdamage accumulates it leads to fracture failure, notably in osteoporosis. Detection methods, based on chelating fluorochromes and radiopaque agents, will enable microdamage to be quantified and, along with bone mass, aid in fracture prediction and prevention. Mechanobiological principles can be utilised to create tissue engineered bone grafts in cases of bone loss due to trauma, malignancy or resorption.

DOI: 10.3233/THC-2006-144-517

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 359-365, 2006

Authors: Taylor, David | Hazenberg, Jan | Lee, T. Clive

Article Type: Research Article

Abstract: Bone is able to detect its strain environment and respond accordingly. In particular it is able to adapt to over-use and under-use by bone deposition or resorption. How can bone sense strain? Various physical mechanisms have been proposed for the so-called cellular transducer, but there is no conclusive proof for any one of them. This paper examines the theories and evidence, with particular reference to a new theory proposed by the authors, involving damage to cellular processes by microcracks. Experiments on bone samples ex-vivo showed that cracks cannot fracture osteocytes, but that cellular processes which span the crack can be …broken. A theoretical model was developed for predicting the number of broken processes as a function of crack size and applied stress. This showed that signals emitted by fractured processes could be used to detect cracks which needed repairing and to provide information on the overall level of damage which could be used to initiate repair and adaptation responses. Show more

Keywords: Bone, adaptation, cellular transducer, remodelling, microdamage

DOI: 10.3233/THC-2006-144-518

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 367-377, 2006

Authors: Racila, M. | Crolet, J.M.

Article Type: Research Article

Abstract: It is well known that long term behavior of implants depends on bone remodeling. In the absence of a model of this phenomenon, few numerical simulations take into account bone remodeling. Some laws have been proposed but they cannot be used in the essential area surrounding the implant. We propose a multi-scale approach: cortical bone is structured in a hierarchical way consisting of five levels. The cortical part of a given bone is made up of various areas having different physical properties adapted to locally existing conditions. A Bony Elementary Volume denotes the elementary part of such a …zone which constitutes our first level. The other levels are in conformity with our previous studies: osteon, lamella, fibre and fibril. This latter is composed by collagen and hydroxyapatite (Hap) occurring in a viscous liquid containing mineral ions. Mathematical homogenisation theory is used to determine equivalent macroscopic properties of a BEV, knowing the physical properties of collagen and Hap and the architectural description of this bony structure. For improving the performance of our simulation software, a new behavior law has been introduced with no continuity between the various levels. The effect of the fluid at the nanoscopic scale is modeled by a constant pressure. Recent developments allow us to determine the magnitude of various entities at nanoscopic scale from information at the macroscopic level. Realized simulations show that the assumption of constant pressure is not sufficient to characterize the nanoscopic mechanical behaviour. This point needs a more complex model with the introduction of a coupling between structure and fluid. This aspect is in development. Show more

DOI: 10.3233/THC-2006-144-519

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 379-392, 2006

Authors: Hazenberg, Jan G. | Taylor, David | Lee, T. Clive

Article Type: Research Article

Abstract: It is well known for almost half a century that bones contain microcracks. Very little is known about the crack growth behaviour of very small cracks, e.g. the stage before they become macroscopically long. The aim of this work was to investigate the dynamic crack growth behaviour of sub-millimetre microcracks in cortical bone. It was found that slow stable crack growth occurs in specimens subjected to static loading conditions. Crack growth direction was dominated by the local fibre orientation of the bones. Crack angles varied between 10 and 36 degrees of the long axis of the bone. Short cracks were …found to show periods of rapid growth followed by intervals of temporary crack arrest. Histological analysis showed that crack arrest occurred due to vascular canals in the bone. During these periods of crack arrest, crack opening displacements increased until the local strain was sufficient to overcome these features. These observations indicate a mechanism for growth of small cracks in bone at constant stress, involving microstructural barriers, time-dependent deformation of material near the crack tip and strain-controlled propagation. Show more

Keywords: Microcracks, crack growth, microstructure

DOI: 10.3233/THC-2006-144-520

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 393-402, 2006

Authors: Lenich, A. | Fierlbeck, J. | Al-Munajjed, A. | Dendorfer, S. | Mai, R. | Füchtmeier, B. | Mayr, E. | Hammer, J.

Article Type: Research Article

Abstract: Conventional osteosynthesis of proximal femur fractures is still affected by serious complication rates between 4–18%, even though advanced implant modifications and surgical techniques are common practice. In terms of increasing age and co-morbidity of patients this complication ratio is expected to increase even further in the immediate future. One major reason for implant failure is the decreasing stability potential of the implant due to a loss in mechanical properties of cancellous bone. Therefore, efforts in new intramedulary techniques specifically focus on the load bearing characteristics of the implant by developing new geometries to improve the implant-tissue interface. This …investigation discusses first clinical results of the trochanteric fixation nail TFN (145 patients) and a biomechanical analysis of the blade/femur head interaction under different static loading conditions. The TFN shows promising performance in first clinical results. In the clinical study the overall complication rate was significantly lower compared to other similar osteosynthesis. For the investigation of the biomechanical stability of the helical TFN blade the following experiments were performed: Analysis of the axial load required for insertion of the blade by free rotation; measurement of the corresponding rotation angle for total insertion (32 mm) (n=8); pull-out forces with suppressed rotation (n=4); loads for rotational overwinding of the implant in the fully inserted condition (n=4). All investigations were performed on human femoral heads. The bone mineral densities of the specimens were detected by QCT-scans. Prior to cadaveric testing the experimental set-up was validated (n=8) by the use of synthetic foam blocks (Sawbone® ). Show more

Keywords: Proximal femur, intramedullary osteosynthesis, TFN

DOI: 10.3233/THC-2006-144-521

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 403-409, 2006

Authors: Helwig, P. | Faust, G. | Hindenlang, U. | Kröplin, B. | Eingartner, C.

Article Type: Research Article

Abstract: Static analysis with finite element of a realistic femur nail bone-implant system in a typical proximal femoral fracture under physiological load bearing situations provides results for stress, displacement and strain. The question to be answered is, if simulation with the finite element analysis is able to explain biomechanically clinical observed patterns of failure. Surface-Reconstruction with CT database of a proximal femur and reconstruction with CT based density data was done. Next steps were to unite the bone structure with the Proximal Femoral Nail and to model two relevant fractures (31-A2.2 and A2.3 according AO). After modelling of geometry, …isotropic material behaviour and load application numeric calculation of the femur-nail system with FE-software was performed. FE simulation mainly shows an axial dislocation of the femoral head screw with nearly no dislocation of the antirotation screw. This so-called z-effect therefore means: (1) Tilting of the proximal main fragment around the sagittal axis between the screws and (2) relative movement of both screws in the frontal plane. Relative movement of the two screws against each other could be the reason for implant failure, the so called cut out. Furthermore simulation shows different gliding of the screws explaining the so called z-telescoping. The analyzed stress patterns have to be relativized, because isotropic material behaviour of cancellous bone was assumed. Further examinations for this issue are necessary. Show more

DOI: 10.3233/THC-2006-144-522

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 411-419, 2006

Authors: Cruz, Mauro | Lourenço, Adelino Francisco | Toledo, Elson Magalhães | da Silva Barra, Luis Paulo | de Castro Lemonge, Afonso Celso | Wassall, Thomaz

Article Type: Research Article

Abstract: Statement of problem: Different implant geometries present different biomechanical behaviors and in this context, one arising question is how cuneiform implant geometry compares to clinical successful cylindrical threaded implant geometry. Purpose: The purpose of this work was to study stress distribution around cuneiform and cylindrical threaded implant geometries using three-dimensional finite element stress analysis taking the latter as a reference. Material and methods: A model was generated from a computerized tomography of a human edentulous mandible with implants placed in the left first premolar region. The model was supported by the mastication muscles and by temporomandibular …joint. A vertical load of 100N was applied at the top of each implant in the direction of their long axes. The mandibular boundary conditions were modeled considering the actual muscle supporting system. Taking muscle forces intensities and directions, balance moment equations were employed to assess the system equilibrium. Cortical and medullary bones were assumed to be homogeneous, isotropic and linearly elastic. Results: The analysis provided results for maximum (S1) and minimum (S2) principal stress and Von Mises (SEQV) stress field. For both geometries, the results showed concentration on one side of the neck, smooth stress distribution along the body and no considerable concentration at the apical area. Conclusion: Results showed similar stress distribution pattern for cuneiform and cylindrical threaded geometries. The stresses profiles along the implants length reproduced their morphology. In both occurred stress concentration at one side of the neck and no body or apical stress concentration. Show more

Keywords: Biomechanics, dental implants, dental stress analysis, finite element analysis

DOI: 10.3233/THC-2006-144-523

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 421-438, 2006

Authors: Asbia, S. | Ibbetson, R. | Reuben, R.L.

Article Type: Research Article

Abstract: This work is concerned with the performance, under dynamic compression, of the adhesives used to simulate cementation of gold crowns onto nickel chromium dies. A measurement system, based on the mounting of strain gauges onto the outer surface of the crowns, has been developed, which allows a semi-quantitative estimate of the state of adhesion. A preliminary study was carried out where miniature gauges were bonded onto the buccal, lingual, mesial and distal surfaces of gold crowns cast to fit onto a chromium-cobalt die, as a precursor to the final design of the instrumented crown. The crowns were then loaded in …compression periodically measuring the strain at all four gauges. The results showed the load-strain relationship in fully, partially and uncemented crowns, along with repeated load-unload behaviour to close to the ultimate strength of the bond. The load-strain relationship is linear and repeatable and the slope varies over a factor of about 30 between the un-cemented and fully cemented crown, demonstrating that there is significant sensitivity to bond integrity. These results were used to determine the parameters for a systematic study of S-N relationships in restorative dentistry crowns. Show more

Keywords: Restorative dentistry, adhesives, mechanical testing

DOI: 10.3233/THC-2006-144-524

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 439-448, 2006

Authors: Karoglan, M. | Schütz, K. | Schieferstein, H. | Horch, H.-H. | Neff, A.

Article Type: Research Article

Abstract: The development of new methods and materials for osteosynthesis requires in vitro testing prior to clinical use to exclude major problems or difficulties. In the field of oral and maxillofacial surgery no standardized testing procedures have so far been established. From a biomechanical point of view the lower jaw can be described as a lever that during the chewing cycle various forces at various points of the bone act upon. Standardized solid foam polyurethane mandibles (Sawbones®, Malmö, Sweden) were used for the testing of various types of screws and different types of fractures. Via linkages that were connected to hydraulic …cylinders defined forces were exerted on the polyurethane mandibles and the deformation was registered depending on the force. Monitoring was carried out contactless and therefore without back coupling by the use of a video system that recorded well-defined points on both sides of the fracture line. The photographs were then evaluated by special software (SIMI MOTION CAPTURE®). The control of the cylinders was performed through a processor that besides static forces also allowed dynamic testing (e.g. sinusoid oscillation with defined amplitude and number of cycles). For the standardized and realistic three-dimensional static or dynamic testing of new methods and materials for osteosynthesis of the lower jaw this test stand has proved to be optimally suitable. Independent on the type of fracture and the material used the field of application for our test stand is the complete lower jaw. Therefore an ethically correct and economically reasonable testing of industrial products and clinical methods of osteosynthesis can be performed with this simulator. Show more

DOI: 10.3233/THC-2006-144-525

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 449-455, 2006

Authors: Carvalho, L. | Moreira, R.A.S. | Simões, J.A.

Article Type: Research Article

Abstract: The performance of a tooth replacement by using a dental implant relies on the mechanical and biological capability of the anatomical substitute to restore lost physiological functions. The design of an implant device able to properly replace the physiological tooth requires the study of the load transfer mechanism at the implant-bone interface and the understanding of the relevance of the periodontal ligament (PDL) in this mechanism. The PDL is a connective soft tissue that provides the fixation of the tooth in its bone-socket and the attenuation of occlusal loads. It also provides the ground cells that are involved in the …remodelling process, induced by a change in the stress-strain pattern of the alveolar bone and also in the cementum of the tooth root. The purpose of this study was to determine the PDL effects on the dynamic load transfer mechanism, from the tooth to the alveolar bone, evaluating the equivalent dynamic stiffness of the ligament structure. A porcine fresh mandible with a tooth was used within the study, applying an experimental procedure to identify the dynamic transmissibility of the entire system. The transmissibility function provided information about the stiffness and damping of the PDL, information that can assist the design of an improved dental implant system. Show more

DOI: 10.3233/THC-2006-144-526

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 457-465, 2006