Incidence of the boundary condition between bone and soft tissue in a finite element model of a transfemoral amputee.

BACKGROUND: Many finite element investigations have been made in the field of lower limb prosthetics; however, friction between bone and soft tissues as a boundary condition has not been considered. OBJECTIVES: To establish whether the change in the contact boundary condition between bone and soft tissues in a transfemoral amputee affects the stress-strain state on the residual limb. STUDY DESIGN: Finite element analysis comparison. METHODS: Finite element models of four transfemoral amputees were developed. In these models the socket, soft tissues and femur were included and two simulations were made for each model, in one of them the interaction between bone and soft tissues was defined as tied (there is no relative displacement between surfaces) and in the other it was defined as a friction boundary condition. RESULTS: The von Mises stress and strain peaks are higher when the friction definition is used than for tied contact definition. The distribution pattern of stresses and strains also change when the contact definition varies from tied to friction. CONCLUSIONS: It was concluded that the friction between bone and soft tissues have a significant impact on the results of finite element models of lower limb prosthetic systems, and therefore in its predictive capabilities. Clinical relevance Understanding the bone-soft tissue interaction can lead to more realistic and accurate finite element models used to predict the stress-strain state in the residual limb of prosthetic users and therefore predict the occurrence of deep tissue injuries.

Analysis of bone demineralization due to the use of exoprosthesis by comparing Young's modulus of the femur in unilateral transfemoral amputees.

BACKGROUND: There is a relation between Hounsfield units obtained from computed tomography (CT) scans and bone density. The density of the bones can be used to establish its mechanical properties and therefore to assess the bone mechanical condition using CT images. OBJECTIVES: To identify the effect of the transfemoral amputation and the use of external lower limb prosthesis in the bone properties, by comparing Young's modulus. STUDY DESIGN: Young's modulus comparison. METHODS: Comparison of bone density between the healthy femur and the amputated bone of 20 unilateral transfemoral amputees was done by generating three histograms of the Hounsfield units at different parts of the femur. The histograms were created based on images obtained by CT and the Hounsfield units were translated to Young's modulus to establish the comparison. RESULTS: The results show a significant difference (p-value <0.05) between the mean value of Young's modulus of healthy and amputated bone. CONCLUSIONS: There is clearly a direct association between the use of external prosthesis and the bone demineralization due the stress shielding phenomenon. The Young's modulus comparison using information from CT images can be a suitable tool to analyze the bone demineralization due to the use of exoprosthesis.

Aplicación de la metodología qfd para la determinación de los requerimientos de diseño de un dispositivo para transladar discapacitados / qfd methodology appliaction to determinate design requeriments for a transportation device for people with disabilities

Frente a la problemática de traslados de pacientes con algún grado de discapacidad se encuentra la necesidad del uso de elementos que la solucionen. En el mercado se encuentran gran cantidad de dispositivos especializados en esta aplicación, pero no cumplen la totalidad de las características y deseos que los clientes esperan. Es por esto que aquí se presenta el desarrollo metodológico de la obtención de las características de diseño de un dispositivo para trasladar discapacitados. Este desarrollo se realizó con base en la metodología de diseño QFD (Despliegue de la Función de la Calidad), con la cual fue posible expresar todos los deseos y requerimientos del cliente en términos mensurables de ingeniería

Alfuzosin improves penile erection triggered by apomorphine in spontaneous hypertensive rats.

OBJECTIVES: Growing evidence suggest that BPH is a risk factor for ED. Since alfuzosin is a cornerstone in the treatment of BPH patients, we assessed the effect of alfuzosin on erectile function in rats when combined with a pro-erectile drug such as apomorphine. METHODS: Potencies of alfuzosin, apomorphine or the combination to relax norepinephrine (NE) precontracted corpus cavernosum tissue of spontaneous hypertensive rats (SHR) were determined. In anaesthetized rats, intracavernous and blood pressures were recorded after administration of apomorphine (10-250microg/kg s.c.) and alfuzosin (3-30microg/kg i.v.). RESULTS: Alfuzosin fully relaxed the NE-precontracted penile tissue (pIC(50)=6.62+/-0.7) while apomorphine, up to 10microM, did not produce any relaxation. The potency of alfuzosin to relax erectile tissue was not further enhanced with 10microM apomorphine. Apomorphine induced erections in rat while alfuzosin alone did not. However, alfuzosin (30microg/kg) significantly enhanced the potency of apomorphine, to induce erections (ED(50)=25microg/kg versus 57microg/kg). In addition, alfuzosin even at 3microg/kg, significantly increased the intracavernous pressure (ICP) during erectile events up to 52-55mmHg when compared to ICP values of 29mmHg with 50microg/kg apomorphine alone. CONCLUSION: These results show that alfuzosin enhances the number and amplitude of erections induced by apomorphine in SHR. Therefore, clinical evaluation of alfuzosin in association with apomorphine is warranted.