RESUMO
With the aim of providing information for modelling joint and limb systems, widely available constitutive hyperelastic laws are evaluated in this paper for their ability to predict the mechanical responses of normal and osteoarthritic articular cartilage. Load-displacement data from mechanical indentation were obtained for normal and osteoarthritic cartilage at 0.1 s(-1) and 0.025 s(-1) and converted to the stress-stretch ratio. The data were then fitted to the Arruda-Boyce, Mooney-Rivlin, neo-Hookean, Ogden, polynomial, and Yeoh hyperelastic laws in the MATLAB environment. Although each of the hyperelastic laws performed satisfactorily at the higher rate of loading, their ability to fit experimental data at the lower loading rate varied considerably. For the preferred models, coefficients were provided for stiff, soft, and average tissues to represent normal and degraded tissue at high and low loading rates. The present authors recommend the use of the Mooney-Rivlin or the Yeoh models for describing both normal and degraded articular cartilage, with the Mooney-Rivlin model providing the best compromise between accuracy and required computational power.
Assuntos
Cartilagem Articular/fisiopatologia , Modelos Biológicos , Osteoartrite/fisiopatologia , Simulação por Computador , Módulo de Elasticidade , Humanos , Valores de Referência , Estresse MecânicoAssuntos
Envelhecimento , Atitude Frente a Saúde , Alocação de Recursos , Idoso , Idoso de 80 Anos ou mais , Envelhecimento/fisiologia , Envelhecimento/psicologia , Serviços de Saúde Comunitária , Eutanásia Ativa , Alocação de Recursos para a Atenção à Saúde , Política de Saúde , Recursos em Saúde , Serviços de Saúde para Idosos , Humanos , Expectativa de Vida , Longevidade , Obrigações Morais , Morbidade , Casas de Saúde/economia , Medicina Preventiva , Política Pública , Qualidade de Vida , Reabilitação , Justiça Social , Responsabilidade Social , Sociologia , Estresse PsicológicoAssuntos
Acessibilidade aos Serviços de Saúde , Direitos Humanos , Alocação de Recursos , Justiça Social , Fatores Etários , Idoso , Análise Custo-Benefício , Teoria Ética , Serviços de Saúde para Idosos/economia , Serviços de Assistência Domiciliar , Humanos , Assistência Médica , Seleção de Pacientes , Medição de Risco , Responsabilidade Social , Estados UnidosRESUMO
In recent years, critics have argued that, when inter-generational transfer programs such as Medicare are judged by the standard of "generational equity", these programs are seen to be unfair. It is argued that, under a pay-as-you-go system, future generations are committed to burdens without their consent; that claims are not contractually guaranteed; that early entrants reap windfalls gains; that successive cohorts are tempted to provide insupportably high benefit levels; and, finally, that fluctuations leave future generations at unacceptable risk. Attempts have been made to defend social insurance programs by means of a "lifespan prudential model" of age-group resource allocation, but this defense does not adequately take account of uncertainties and inequities faced by historical birth cohorts. A deeper defense must acknowledge an element of risk-sharing and solidarity while trying to limit inequities within reasonable bounds.