Bone cutting is widely used in orthopaedic, dental and neuro surgeries and is a technically demanding surgical procedure. Novel surgical methods are continually introduced in orthopaedic, neuro and dental surgeries and are aimed at minimising the invasiveness of the operation and allowing more precise cuts. One such method that utilises cutting with superimposed ultrasonic vibration is known as ultrasonically- assisted cutting (UAC). The main concern in bone cutting is the mechanical and thermal damage to the bone tissue induced by high-speed power tools. Recent technological improvements are concerned with the efforts to decrease the force required by the surgeon when cutting the bone as well as increases in surgery speed. A programme of experiments was conducted to characterise properties of a bone and get a basic understanding of the mechanics of bone cutting. The experiments included: (a) nanonindentation and tension tests to obtain the properties for the finite element (FE) bone cutting model, (b) high-speed filming to observe the chip formation process, which influences thermomechanics of the cutting process in conventional drilling (CD) and ultrasonically-assisted drilling (UAD) and, (c) plane cutting and drilling experiments to measure the levels of force and temperature rise in the bone tissue. Novel two-dimensional finite element (FE) models of cortical bone cutting were developed for conventional and ultrasonically-assisted modes with the MSC.MARC general FE code that provided thorough numerical analysis of thermomechanics of the cutting process. Mechanical properties such as the elastic modulus and strain-rate sensitivity of the bone material were determined experimentally and incorporated into the FE models. The influence of cutting parameters on the levels of stress, penetration force and temperature in the bone material was studied using conventional cutting (CC) and ultrasonically-assisted cutting (UAC). The temperature rise in the bone material near the cutting edge was calculated and the effect of cutting parameters on the level of thermal necrosis was analysed. The necrosis depth in bone was calculated as a distance from the cut surface to the point where the thermal threshold level was attained. Comparative studies were performed for the developed FE models of CC and UAC of bone and the results validated by conducting experiments and using data from scientific publications. The main outcome of the thesis is an in-depth understanding of the bone cutting process, and of its possible application in orthopaedics. Recommendations on further research developments are also suggested.

Cette thèse concerne la segmentation d’images HRpQCT et l’évaluation d’indices morphologiques de l’os cortical pour le diagnostic de l’ostéoporose et la prédiction des fractures osseuses. Dans un premier temps,deux méthodes sont proposées pour la segmentation de l’os cortical. La première utilise une nouvelle approche des contours actifs basée sur la logique floue suivie d’une nouvelle technique de remplissage développée pour imiter le comportement des opérateurs pour séparer l’os cortical de l’os trabéculaire. La deuxième approche est une technique 3D à double contours actifs combinant à la fois les informations locales le long et entre les deux contours. Les deux approches de segmentation sont comparées à celles de l’état de l’art afin de valider leurs performances. Dans un second temps, différents indices extraits de l’os cortical sont utilisés pour déterminer leur potentiel de prédiction des fractures ostéoporotiques. Les résultats obtenus montent que l’analyse globale de l’os cortical masque des variations potentiellement importantes.Par conséquent, une décomposition régionale de l’enveloppe corticale est proposée afin d’améliorer la prédiction du risque fracturaire. / This thesis concerns the segmentation of HRpQCT images and the evaluation of the cortical bone parameters for the osteoporosis characterization and the fracture prediction. Firstly, two approaches were proposed to segment the cortical bone. The first uses a new fuzzy energy active contours approach followed by a new filling technique designed to mimic the behaviour of clinicians while extracting the cortical bone from the trabecularone. The second approach is a local based 3D dual active contours approach proposed to separate between three regions constituting the image. To move, this approach combines the local information along each point in the two contours conjointly with the information between them. The segmentation results of these approaches were confronted to the state of the art methods to validate their performance. Secondly,different parameters were extracted from the segmented cortical bone to monitor the association of these parameters with the osteoporotic fracture prediction. Global analysis of the cortical bone obscures potentially important regional variations. Therefore, regional cortical decomposition was proposed to illustrate that cortical sub-regions could improve the evaluation of fracture risk than the global analysis of the cortical bone.

O conhecimento das propriedades dielétricas do osso tem se mostrado importante na medicina ortopédica para aplicações em diagnóstico e tratamento da osteoporose, de fraturas, controle da osteonecrose e, também, na área de cerâmicas industriais (porcelana de osso). Neste trabalho, apresenta-se uma metodologia de avaliação das permissividades complexas de osso cortical de fêmur bovino desidratado, utilizando-se o método de impedância em uma linha de transmissão. Esta se constitui de um condutor coaxial, do tipo N, de uma porta, e um terminal aberto, que é conectado a um analisador de impedância. A faixa de freqüência considerada está compreendida entre 100 Hz e 1 MHz. Em particular, apresenta-se uma metodologia de caracterização dielétrica de osso, com ênfase nas avaliações das suas características anisotrópicas. Alguns resultados das propriedades dielétricas são comparados com os valores experimentais e teóricos disponíveis na literatura. Este procedimento é justificado, haja vista que os valores experimentais encontrados na literatura são esparsos e pontuais, quando se considera toda a faixa do espectro eletromagnético avaliado. Ressalta-se que não existe um consenso entre especialistas da área sobre a precisão e metodologia de obtenção destes. O mesmo ocorre com relação aos protocolos de medição propostos nas normas internacionais, em particular, quando se buscam padrões de avaliações de materiais biológicos sólidos. Os valores da permissividade obtidos com as medidas realizadas entre 100 Hz e 1 MHz evidenciam a presença de uma anisotropia efetiva, sendo esta característica ressaltada em freqüências da ordem de algumas dezenas de kHz. Embora o fenômeno de anisotropia não se manifeste nas faixas superiores à anteriormente mencionada, algumas medidas foram realizadas, também, numa faixa de freqüências superiores, entre 50 MHz e 3 GHz. Utilizou-se um analisador de redes conectado a um dispositivo coaxial de duas portas, visando avaliar a adequabilidade dos procedimentos de preparação do tecido ósseo na avaliação das características de materiais biológicos em altas freqüências, já que se dispunha da instrumentação necessária e de alguns resultados, obtidos na literatura, para sua validação. / The knowledge of the dielectric properties of bones has become important to orthopedic therapy, for applications in the diagnosis and treatment of osteoporosis, fractures, and osteonecrosis, as well as is the industrial ceramics field (bone china). This work proposes a methodology for the evaluation of the complex permittivity of a dehydrated cortical bone of bovine femur, using an impedance method in a transmission line. The transmission line is composed by an one-port open-ended N-type coaxial conductor, connected to an impedance analyzer. The frequency range studied was 100 Hz - 1 MHz. The methodology proposed is proper for the dielectric characterization of bone and this work emphasizes the evaluation of its anisotropic characteristics. Some dielectric properties experimentally found in this work are compared to the experimental and theoretical results available in literature, which are sparse and punctual in the considered electromagnetic spectrum. It is pointed out that there is no agreement among the experts when the subject is the proper measuring methodology and its precision. The same occurs when the subject is the measuring protocols proposed by the international standards, especially for solid biological materials. The permittivity results obtained in frequencies between 100 Hz and 1 MHz evince an effective anisotropy, which stands out in frequencies of a few tens of kHz. Although the anisotropy phenomenon does not occur in a frequency range higher than the one previously mentioned, some measures were taken in the 50 MHz - 3 GHz range for validation, based on results from literature. A network analyzer and a two-port coaxial device were then used in such measures, which aimed the evaluation of the adequacy of the procedure used in the preparation of the bone tissue in high-frequency measurements.

O conhecimento das propriedades dielétricas do osso tem se mostrado importante na medicina ortopédica para aplicações em diagnóstico e tratamento da osteoporose, de fraturas, controle da osteonecrose e, também, na área de cerâmicas industriais (porcelana de osso). Neste trabalho, apresenta-se uma metodologia de avaliação das permissividades complexas de osso cortical de fêmur bovino desidratado, utilizando-se o método de impedância em uma linha de transmissão. Esta se constitui de um condutor coaxial, do tipo N, de uma porta, e um terminal aberto, que é conectado a um analisador de impedância. A faixa de freqüência considerada está compreendida entre 100 Hz e 1 MHz. Em particular, apresenta-se uma metodologia de caracterização dielétrica de osso, com ênfase nas avaliações das suas características anisotrópicas. Alguns resultados das propriedades dielétricas são comparados com os valores experimentais e teóricos disponíveis na literatura. Este procedimento é justificado, haja vista que os valores experimentais encontrados na literatura são esparsos e pontuais, quando se considera toda a faixa do espectro eletromagnético avaliado. Ressalta-se que não existe um consenso entre especialistas da área sobre a precisão e metodologia de obtenção destes. O mesmo ocorre com relação aos protocolos de medição propostos nas normas internacionais, em particular, quando se buscam padrões de avaliações de materiais biológicos sólidos. Os valores da permissividade obtidos com as medidas realizadas entre 100 Hz e 1 MHz evidenciam a presença de uma anisotropia efetiva, sendo esta característica ressaltada em freqüências da ordem de algumas dezenas de kHz. Embora o fenômeno de anisotropia não se manifeste nas faixas superiores à anteriormente mencionada, algumas medidas foram realizadas, também, numa faixa de freqüências superiores, entre 50 MHz e 3 GHz. Utilizou-se um analisador de redes conectado a um dispositivo coaxial de duas portas, visando avaliar a adequabilidade dos procedimentos de preparação do tecido ósseo na avaliação das características de materiais biológicos em altas freqüências, já que se dispunha da instrumentação necessária e de alguns resultados, obtidos na literatura, para sua validação. / The knowledge of the dielectric properties of bones has become important to orthopedic therapy, for applications in the diagnosis and treatment of osteoporosis, fractures, and osteonecrosis, as well as is the industrial ceramics field (bone china). This work proposes a methodology for the evaluation of the complex permittivity of a dehydrated cortical bone of bovine femur, using an impedance method in a transmission line. The transmission line is composed by an one-port open-ended N-type coaxial conductor, connected to an impedance analyzer. The frequency range studied was 100 Hz - 1 MHz. The methodology proposed is proper for the dielectric characterization of bone and this work emphasizes the evaluation of its anisotropic characteristics. Some dielectric properties experimentally found in this work are compared to the experimental and theoretical results available in literature, which are sparse and punctual in the considered electromagnetic spectrum. It is pointed out that there is no agreement among the experts when the subject is the proper measuring methodology and its precision. The same occurs when the subject is the measuring protocols proposed by the international standards, especially for solid biological materials. The permittivity results obtained in frequencies between 100 Hz and 1 MHz evince an effective anisotropy, which stands out in frequencies of a few tens of kHz. Although the anisotropy phenomenon does not occur in a frequency range higher than the one previously mentioned, some measures were taken in the 50 MHz - 3 GHz range for validation, based on results from literature. A network analyzer and a two-port coaxial device were then used in such measures, which aimed the evaluation of the adequacy of the procedure used in the preparation of the bone tissue in high-frequency measurements.

Este estudo investiga o Módulo de Young (Módulo de Elasticidade) em amostras de osso cortical oriundas de uma mesma região da tíbia bovina depois de submetidas a congelamentos e descongelamentos sucessivos. As amostras foram coletadas da face caudal do terço médio da diáfise de tíbias bovinas e depois submetidas a testes de flexão em três pontos e ensaios de ruptura, obedecendo à norma ASTMD790M86ε1. Nesse experimento, 20 pares de amostras de ossos corticais foram retirados de 20 tíbias bovinas, cada amostra medindo 2 mm x 4 mm x 40 mm, aproximadamente. Todos os testes foram realizados à temperatura controlada (21 graus Celsius), e as condições de ensaio foram as mesmas durante os testes. As amostras foram identificadas e divididas em dois grupos experimentais: Grupo A: as amostras foram conservadas (em sacos plásticos) a - 20 graus Celsius (submetidos a congelamentos e descongelamentos sucessivos por 50 vezes: uma vez ao dia durante 50 dias). Esses descongelamentos produziram 15 ensaios de flexão, sendo que o primeiro foi realizado com as amostras ainda frescas mantidas em geladeira a 4 graus Celsius. Após os 50 descongelamentos foram levados até a ruptura. Grupo B: as amostras foram conservadas frescas (em sacos plásticos) a 4 graus Celsius em geladeira aguardando o tempo para que os ensaios do grupo A fossem concluídos e, posteriormente fez-se o teste de ruptura. Importantes cuidados foram tomados. Depois de cada descongelamento, as amostras foram analisadas e comparadas com as amostras frescas tanto para os ensaios de flexão em três pontos como para os ensaios de ruptura. Observamos que o congelamento não alterou de modo significativo as propriedades mecânicas destes ossos, pois não foi encontrada nenhuma diferença significativa entre o comportamento dos dois grupos testados. Isso implica que, congelando e estocando mesmo por longos períodos, as propriedades mecânicas não se alteram tanto nos ensaios de flexão em três pontos como nos ensaios de ruptura. Com respeito às diferenças observadas no dia a dia, as alterações do primeiro dia até o último dia não foram significativas / The present study was conducted to investigate the Young Module (Elasticity Module) in cortical bone samples submitted to successive freezing and thawing and then assayed in flexion tests at three points and in rupture tests according to the norms of ASTMD790M86ε1. Twenty pairs of cortical bone samples, each measuring approximately 2 x 4 x 40 mm, were collected from the same region of the caudal surface of the middle third of the diaphysis of 20 bovine tibiae and divided into two experimental groups: Group A: consisting of 20 cortical bone samples stored at – 20 Celsius degrees in plastic bags and submitted to successive freezing and thawing 50 times once a day for 50 days. These thawing episodes produced 15 flexion assays. After the 50 thawing episodes, the samples were tested until rupture. Group B: consisting of 20 cortical bone samples stored at 4 Celsius degrees in plastic bags in a refrigerator until the time when the assays of group A were concluded and then submitted to the rupture test. No statistically significant variation in the Young Module was observed after the flexion test at three points performed for Group A. The values of rupture tension also did not differ significantly between groups A and B. We observed that freezing did not cause a significant change in the mechanical properties of these bones, indicating that freezing and storage of these bones even for long periods of time does not alter their mechanical properties in flexion tests at three points or in rupture assays

A osteoporose é um enfraquecimento progressivo dos ossos, que ficam cada vez mais sujeitos a fraturas. Embora possa acometer ambos os sexos, ela é mais freqüente nas mulheres após a menopausa devido à diminuição dos hormônios femininos, os estrógenos. É uma doença que avança lentamente, sem sintomas, geralmente sem ser percebida até que aconteça uma fratura. Uma vez instalada a osteoporose, tem que se evitar maior perda óssea para prevenir fraturas. O objetivo deste trabalho é analisar o quadro de instalação de osteopenia em ossos corticais de ratas ovariectomizadas. Foi utilizado um modelo de osteopenia em 29 ratas Wistar ovarectomizadas com massa corpórea de 250 gramas. Os animais foram divididos em 6 grupos experimentais e eutanaziados em períodos diferentes: o primeiro grupo foi eutanaziado 30 dias após a cirurgia, que corresponde ao tempo de início da osteopenia, e a partir daí, os demais grupos foram eutanaziados numa seqüência de 15 dias até o 105º dia. A avaliação do quadro de instalação foi realizada através de medidas antropométricas e de propriedades mecânicas dos fêmures (ensaio de flexão de três pontos). Cada um dos itens obtidos foram comparados utilizando-se o programa GraphPad InStat 3. O teste t-Student foi aplicado para checar a variação do peso corporal com p < 0,05. Aplicaram-se os testes ANOVA e Student-Newmam-Keuls com coeficiente de variação também menor que 5% para os demais itens analisados. Observou-se um aumento significativo no comprimento dos fêmures durante o primeiro mês de experimento, assim como na carga máxima aplicada. Os resultados obtidos neste estudo sugerem que a ovariectomia é um fator que não causa grandes alterações mecânicas e geométricas na região cortical dos fêmures de ratas no período analisado / Osteoporosis is a progressive weakness of bones, which are more and more subjects to fractures. Although it happens to men and women, it is more frequent in postmenopausal women due to a decrease of female hormones. It is a disease without symptoms and it is usually noticed only after a fracture. Once the osteoporosis is installed, a bigger bone loss must be avoided in order to prevent a fracture. This study aims to analyze the osteopenia installation process in cortical bones of ovariectomized rats. An osteopenia model was used in 29 ovariectomized Wistar female rats with body weight of 250 g. Animals were divided in 6 experimental groups, the first group was sacrificed 30 days after the surgery and, the other groups, every 15 days on until the 105th day. The evaluation of installation process was made through anthropometrics and mechanical proprieties of femur (three-point bending test). Program GraphPad InStat 3 was used in order to compare the observed items. T-student test was used to check the body weight variation with p < 0,05 and tests ANOVA and Student-Newmam-Keuls were applied to the other items (p < 0,05). A significant increase in femur length and in maximum bending load were obtained. The found results in this research suggest that ovariectomy is a factor that does not cause significant mechanical and geometric alterations on cortical region of femurs in female rats during the analyzed period

Weak and osteoporotic bones are an increasing cause of mortality and painful physical impairment among the elderly, especially in the Western world. Bone mineral density (BMD, g/cm2) accrual during childhood and adolescence is thought to influence an individual’s risk of osteoporosis and the related fractures. A main aim of this thesis is to investigate the effects that various types of weight-bearing physical activity have on bone accretion in young males during their active sports careers and to study the effects that detraining has on BMD. The results suggest that bone is sensitive to loading after puberty in males, and important gains in BMD stemming from physical activity were observed during the 12-year follow-up period (papers I-III). These gains seem to be site-specific and related to the type and amount of physical activity in which individuals participate (papers I-III). For example, badminton, a sport that is characterized by jumps and rapid versatile moments in multiple directions was associated with greater gains in BMD than ice hockey was. In addition, our results indicate that with reduced training, exercise-induced bone benefits decline, predominantly at trabecular sites (paper II). In contrast, high bone density attained from previous physical loading was partially preserved at cortical bone sites after about eight years of reduced activity (papers I-II). In study IV, the associations between self-perceived health, BMD, and other lifestyle factors were studied in a well-defined group of women and men of varying ages. We found that self-perceived health was related to several lifestyle factors, such as physical activity, which were also related to BMD at the femoral neck. In summary, BMD in young males seem to be especially sensitive to activities associated with supposed high strains in unusual directions at specific bone sites. A high bone density stemming from previous weight-bearing physical activity is largely lost at trabecular bone sites with reduced physical activity levels. Finally, self-perceived health seems to be associated with several lifestyle factors that are also associated with BMD at the femoral neck.

No description available.

The Finite Element Method of stress analysis is employed in axisymmetric, two and three-dimensional forms, to investigate the mechanical behaviour of dental structures under simulated oral loading conditions. Stress distributions which are examined, include those occuring in the crowns of normal teeth due to masticatory loading and in restored teeth as a consequence of the restoration's setting and thermal expansions. The force distributions occuring on roots of individual teeth and on teeth used as abutments for various bridge constructions are also investigated for both axial and non-axial loading and various alveolar bone support conditions. The instantaneous centres of rotation of teeth when subjected to orthodontic loading are also determined. The Finite Element Method is employed to examine various published hypotheses which attempt to correlate the mechanical behaviour of bone structures with that tissue's biological response characteristics. The cases examined include the remodelling of the alveolar process subsequent to orthodontic treatment and the remodelling or so-called straightening of the malaligned long bone. Utilising published experimental data, the Finite Element Method is also employed in a reverse mode to enable some hitherto unknown mechanical properties of the periodontal membrane and cortical bone tissues to be determined. Indeed, due to the flexibility of the method, it was possible to represent these tissues as orthotropic materials. The work is presented in two volumes. While the first volume contains all the results of the analyses, the second contains an outline of the relevant finite element theory. Nevertheless, where the theory has been extended, in particular in the area of non-isotropic material analysis, it is developed in greater depth. The second volume also contains both a thorough description and a listing of all the computer programs developed.

Hip fracture has been identified as one of the main health problems in the elderly. To improve the accuracy in assessing subject-specific hip fracture risk, this study proposed normalized cortical bone thickness (NCBT) estimated from patient’s hip DXA as an alternative predictor of hip fracture risk. Hip fracture risk index (HFRI) derived from DXA-based finite element model was utilized as a baseline for evaluating the effectiveness of NCBT in predicting hip fracture risk. It was found that NCBT at the lateral side of the narrowest femoral neck had the strongest correlation with femoral neck HFRI among the six locations of the proximal femur. This study suggests that it is possible to use NCBT as a surrogate for a quick evaluation of hip fracture risk. Yet its clinical performances such as sensitivity to therapy effectiveness and the ability to discriminate clinical fracture cases will be investigated in a future study.