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Castel Guelfo di Bologna, Italy

Schileo E.,Laboratorio Of Bioingegneria Computazionale | Balistreri L.,Laboratorio Of Tecnologia Medica | Grassi L.,Laboratorio Of Tecnologia Medica | Cristofolini L.,University of Bologna | Taddei F.,Laboratorio Of Tecnologia Medica
Journal of Biomechanics

Proximal femur strength estimates from computed tomography (CT)-based finite element (FE) models are finding clinical application. Published models reached a high in-vitro accuracy, yet many of them rely on nonlinear methodologies or internal best-fitting of parameters. The aim of the present study is to verify to what extent a linear FE modelling procedure, fully based on independently determined parameters, can predict the failure characteristics of the proximal femur in stance and sideways fall loading configurations.Fourteen fresh-frozen cadaver femora were CT-scanned. Seven femora were tested to failure in stance loading conditions, and seven in fall. Fracture was monitored with high-speed videos. Linear FE models were built from CT images according to a procedure already validated in the prediction of strains. An asymmetric maximum principal strain criterion (0.73% tensile, 1.04% compressive limit) was used to define a node-based risk factor (RF). FE-predicted failure load, mode (tensile/compressive) and location were determined from the first node reaching RF=1.FE-predicted and measured failure loads were highly correlated (R2=0.89, SEE=814N). In all specimens, FE models correctly identified the failure mode (tensile in stance, compressive in fall) and the femoral region where fracture started (supero-lateral neck aspect). The location of failure onset was accurately predicted in eight specimens.In summary, a simple FE model, adaptable in the future to multiple loads (e.g. including muscles), was highly correlated with experimental failure in two loading conditions on specimens ranging from normal to osteoporotic. Thus, it can be suitable for use in clinical studies. © 2014 Elsevier Ltd. Source

Taddei F.,Laboratorio Of Tecnologia Medica | Palmadori I.,Laboratorio Of Tecnologia Medica | Taylor W.R.,ETH Zurich | Heller M.O.,University of Southampton | And 3 more authors.
Journal of Biomechanics

It has been suggested that the mechanical competence of the proximal femur is preserved with respect to physiological loading conditions rather than accidental overloading, but the consequences of this adaptation for fracture risk in the elderly remain unclear. The goal of the present study was to analyse the safety factor of the human femur in the two most frequent daily activities, level walking and stair climbing, and to understand the dependence, if any, of this safety factor on age, volumetric bone mineral density (vBMD), and gender.To this aim, a finite element study was performed on 200 subjects (116 women and 84 men), spanning a large range of age (23-84 years) and vBMD levels (. T-score from 0 to -3.59). For the first time, finite element models that included a subject-specific description of the anatomy and mineral density distribution of each bone were coupled with a personalisation of the loads acting on the proximal femur during movement, including the action of the muscles and their variability across the population.The results demonstrate that the human proximal femur is characterised by a high safety factor (on average five, never reaching fracture threshold), even in the presence of advanced age and low mineral content. These results corroborate the hypothesis that the relationship between loading and mechanical competence is generally preserved in the elderly population for the most frequent motor activities, walking and stair climbing. Interestingly, a decrease of the safety factor was observed with increasing lifespan and reduced mineral content in women but not in men. © 2014 Elsevier Ltd. Source

Viceconti M.,Laboratorio Of Tecnologia Medica | Taddei F.,Laboratorio Of Tecnologia Medica | Cristofolini L.,Laboratorio Of Tecnologia Medica | Cristofolini L.,University of Bologna | And 3 more authors.
Journal of Biomechanics

Elderly frequently present variable degrees of osteopenia, sarcopenia, and neuromotor control degradation. Severely osteoporotic patients sometime fracture their femoral neck when falling. Is it possible that such fractures might occur without any fall, but rather spontaneously while the patient is performing normal movements such as level walking? The aim of this study was to verify if such spontaneous fractures are biomechanically possible, and in such case, which conditions of osteoporosis, sarcopenia, and neuromotor degradation could produce them. To the purpose, a probabilistic multiscale body-organ model validated against controlled experiments was used to predict the risk of spontaneous fractures in a population of 80-years old women, with normal weight and musculoskeletal anatomy, and variable degree of osteopenia, sarcopenia, and neuromotor control degradation. A multi-body inverse dynamics sub-model, coupled to a probabilistic neuromuscular sub-model, and to a femur finite element sub-model, formed the multiscale model, which was run within a Monte Carlo stochastic scheme, where the various parameters were varied randomly according to well defined distributions. The model predicted that neither extreme osteoporosis, nor extreme neuromotor degradation alone are sufficient to predict spontaneous fractures. However, when the two factors are combined an incidence of 0.4% of spontaneous fractures is predicted for the simulated population, which is consistent with clinical reports. When the model represented only severely osteoporotic patients, the incidence of spontaneous fractures increased to 29%. Thus, is biomechanically possible that spontaneous femoral neck fractures occur during level walking, due to a combination of severe osteoporosis and severe neuromotor degradation. © 2011 Elsevier Ltd. Source

Grassi L.,Laboratorio Of Tecnologia Medica | Schileo E.,Laboratorio Of Bioingegneria Computazionale | Taddei F.,Laboratorio Of Tecnologia Medica | Zani L.,Laboratorio Of Tecnologia Medica | And 6 more authors.
Journal of Biomechanics

Subject-specific finite element models have been used to predict stress-state and fracture risk in individual patients. While many studies analysed quasi-axial loading configurations, only few works simulated sideways load configurations, such as those arising in a fall. The majority among these latter directly predicted bone strength, without assessing elastic strain prediction accuracy. The aim of the present work was to evaluate if a subject-specific finite element modelling technique from CT data that accurately predicted strains in quasi-axial loading configurations is suitable to accurately predict strains also when applying low magnitude loads in sideways configurations. To this aim, a combined numerical-experimental study was performed to compare finite element predicted strains with strain-gauge measurements from three cadaver proximal femurs instrumented with sixteen strain rosettes and tested non-destructively under twelve loading configurations, spanning a wide cone (0-30° for both adduction and internal rotation angles) of sideways fall scenarios. The results of the present study evidenced a satisfactory agreement between experimentally measured and predicted strains (R 2 greater than 0.9, RMSE% lower than 10%) and displacements. The achieved strain prediction accuracy is comparable to those obtained in state of the art studies in quasi-axial loading configurations. Still, the presence of the highest strain prediction errors (around 30%) in the lateral neck aspect would deserve attention in future studies targeting bone failure. © 2011 Elsevier Ltd. Source

Grassi L.,Laboratorio Of Tecnologia Medica | Schileo E.,Laboratorio Of Bioingegneria Computazionale | Boichon C.,ANSYS Inc. | Viceconti M.,University of Sheffield | Taddei F.,Laboratorio Of Tecnologia Medica
Medical Engineering and Physics

Computed tomography (CT)-based finite element (FE) reconstructions describe shape and density distribution of bones. Both shape and density distribution, however, can vary a lot between individuals. Shape/density indexation (usually achieved by principal component analysis-PCA) can be used to synthesize realistic models, thus overcoming the shortage of CT-based models, and helping e.g. to study fracture determinants, or steer prostheses design. The aim of this study was to describe a PCA-based statistical modelling algorithm, and test it on a large CT-based population of femora, to see if it can accurately describe and reproduce bone shape, density distribution, and biomechanics.To this aim, 115 CT-datasets showing normal femoral anatomy were collected and characterized. Isotopological FE meshes were built. Shape and density indexation procedures were performed on the mesh database. The completeness of the database was evaluated through a convergence study. The accuracy in reconstructing bones not belonging to the indexation database was evaluated through (i) leave-one-out tests (ii) comparison of calculated vs. in-vitro measured strains.Fifty indexation modes for shape and 40 for density were necessary to achieve reconstruction errors below pixel size for shape, and below 10% for density. Similar errors for density, and slightly higher errors for shape were obtained when reconstructing bones not belonging to the database. The in-vitro strain prediction accuracy of the reconstructed FE models was comparable to state-of-the-art studies.In summary, the results indicate that the proposed statistical modelling tools are able to accurately describe a population of femora through finite element models. © 2014 IPEM. Source

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