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1.
Osteoporos Int ; 27(4): 1519-1528, 2016 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-26576543

RESUMO

UNLABELLED: The strength of both femurs was estimated in 198 post-menopausal women through subject-specific finite element models. Important random differences between contralateral femurs were found in a significant number of subjects, pointing to the usefulness of further studies to understand if strength-based classification of patients at risk of fracture can be affected by laterality issues. INTRODUCTION: Significant, although small, differences exist in mineral density and anatomy of contralateral proximal femurs. These differences, and their combined effect, may result in a side difference in femurs' strength. However, this has never been tested on a large sample of a homogenous population. METHODS: The strength of both femurs was estimated in 198 post-menopausal women through CT-derived finite element models, built using a validated procedure, in sideways fall conditions. The impact of the resulting asymmetry on the classification of subjects at risk of fracture was analysed. RESULTS: The small difference observed between sides (the right femur on average 4 % stronger than the left) was statistically significant but mechanically negligible. In contrast, higher random differences (absolute difference between sides with respect to mean value) were found: on average close to 15 % (compared to 9.2 % for areal bone mineral density (aBMD) alone), with high scatter among the subjects. When using a threshold-based classification, the right and left femurs were discordant up to over 20 % of cases (K always lower than 0.60) but the left femur was concordant (mean K = 0.84) with the minimum strength between right and left. CONCLUSION: Considering both femurs may be important when trying to classify subjects at risk of failure with strength estimates. Future studies including fracture assessment would be necessary to quantify the real impact.


Assuntos
Densidade Óssea/fisiologia , Fêmur/anatomia & histologia , Pós-Menopausa/fisiologia , Absorciometria de Fóton/métodos , Idoso , Idoso de 80 Anos ou mais , Feminino , Fêmur/diagnóstico por imagem , Fêmur/fisiologia , Colo do Fêmur/anatomia & histologia , Colo do Fêmur/fisiologia , Análise de Elementos Finitos , Humanos , Pessoa de Meia-Idade , Tomografia Computadorizada por Raios X/métodos , Suporte de Carga/fisiologia
2.
J Biomech ; 45(2): 394-9, 2012 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-22079387

RESUMO

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.


Assuntos
Cabeça do Fêmur/fisiologia , Análise de Elementos Finitos , Modelos Biológicos , Estresse Fisiológico , Cabeça do Fêmur/anatomia & histologia , Cabeça do Fêmur/diagnóstico por imagem , Humanos , Tomografia Computadorizada por Raios X , Suporte de Carga/fisiologia
3.
Med Eng Phys ; 34(2): 161-71, 2012 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-21813311

RESUMO

The biomechanical behaviour of current hip epiphyseal replacements is notably sensitive to the typical variability of conditions following a standard surgery. The aim of the present study was to assess the biomechanical robustness to the variability of post-operative conditions of an innovative proximal epiphyseal replacement (PER) hip device featuring a short, curved and cemented stem. The risk of femoral neck fractures, prosthesis fractures and aseptic loosening were assessed through a validated finite element procedure following a systematic approach. Risk changes due to anatomical variations were assessed mimicking extreme conditions in terms of femoral size and level of osteoporosis. Failure risks associated with surgical uncertainties were assessed mimicking extreme conditions in terms of uncertainties on the prosthesis position/alignment, cement-bone interdigitation depth, and friction between the prosthesis and the hosting cavity. The femoral neck strength increased after implantation from 9% to 49% and was most sensitive to changes of the anatomo-physiological variables. The risk of stem fractures was low in all studied configurations. The risk of stem loosening was low and most sensitive to surgical uncertainties. In conclusion, the new device can be considered an effective alternative to current epiphyseal replacements. Care is recommended in a proper seating of the prosthesis in the femur.


Assuntos
Artroplastia de Quadril/métodos , Análise de Elementos Finitos , Fenômenos Mecânicos , Incerteza , Fenômenos Biomecânicos , Epífises/cirurgia , Fraturas do Colo Femoral , Humanos , Masculino , Pessoa de Meia-Idade , Medicina de Precisão , Falha de Prótese , Reprodutibilidade dos Testes , Medição de Risco
4.
Med Eng Phys ; 33(10): 1203-11, 2011 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-21757392

RESUMO

An innovative epiphyseal device has been recently proposed claiming an effective bone-prosthesis load transfer and a nearly physiological bone stresses distribution. However preliminary experimental tests showed a 23% weakening of the femoral neck after implantation. Aim of this study was to revise the prosthesis geometry with the goal of enhancing the femoral neck strength after implantation, while maintaining unchanged the initial conceptual design. To this aim, the risk of femoral neck fractures, prosthesis fractures, aseptic loosening and excessive bone resorption were addressed through a validated finite element procedure following a systematic approach. The initial prosthesis geometry was revised to reduce each investigated failure risk below the threshold of acceptance (100%). The new geometry was re-assessed to verify the effectiveness of the revision. The first design was predicted to locally induce high bone strains and cement stresses, which translated in a risk of bone and cement failure exceeding the threshold of acceptance (>100%). The revised design preserved a good stability of the device, contemporary reducing the risk for bone (45%) and cement (60%) failure. If results will be confirmed by statistical and clinical experimentations, current clinical indications for hip epiphyseal devices might be extended.


Assuntos
Análise de Elementos Finitos , Quadril , Desenho de Prótese/métodos , Idoso , Idoso de 80 Anos ou mais , Fenômenos Biomecânicos , Epífises , Análise de Falha de Equipamento , Feminino , Fraturas do Colo Femoral/etiologia , Humanos , Funções Verossimilhança , Masculino , Reprodutibilidade dos Testes , Risco
5.
J Oral Rehabil ; 33(9): 674-81, 2006 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-16922741

RESUMO

Experimental devices based on vibration testing are employed as non-destructive procedures for evaluating implants osseointegration. Their behaviour was evaluated considering the outcome of numerical analysis. The purpose was to use the finite element method for assessing the ability of frequency analysis in detecting the degree of oral implant osseointegration. A three-dimensional model of a mandible was obtained from tomographic survey. A single implant was considered in canine region. Two configurations were analysed, with and without a mass linked to the implant as a cantilever, reproducing experimental devices. Simulation consisted of analysing the response to impulse forces for different osseointegration levels, thus evaluating the biomechanical efficiency of the implant-bone compound. A good correlation between frequency response and osseointegration level was obtained. This was carried out by providing an impulse excitation of the implant that resulted in a vibration pattern. Within the limit of finite element analysis, the outcomes showed that numerical investigation provides understanding the behaviour of testing devices based on frequency measurements, confirming the potential of vibrations technique as non-invasive analysis for osseointegration process.


Assuntos
Implantes Dentários , Análise do Estresse Dentário/métodos , Análise Numérica Assistida por Computador , Osseointegração/fisiologia , Fenômenos Biomecânicos , Simulação por Computador , Análise de Elementos Finitos , Humanos , Modelos Teóricos , Vibração
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