Biomedical subjects

J A Simões

Publications and source records attributed to J A Simões.

13 recordsLinked to original sources

PubMed2007

Experimental validation of intact and implanted distal femur finite element models.

Four finite element (FE) models of intact and distal femur of knee replacements were validated relative to measured bone strains. FE models of linear tetrahedrons were used. Femoral replacements with cemented stemless, cemented and noncemented femoral stems of the PFC Sigma Modular Knee System were analyzed. Bone strains were recorded at ten locations on the cortex. The magnitude of the FE bone strains corresponded to the mean measured strains, with an overall agreement of 10%. Linear regression between the FE and mean experimental strains produced slopes between 0.94 and 1.06 and R(2) values between 0.92 and 0.99. RSME values were less than 12%. The FE models were able to adequately replicate the mechanical behavior of distal femur reconstructions.

Biomechanical Phenomena↗

PubMed2006

Tetrahedral versus hexahedral finite elements in numerical modelling of the proximal femur.

The objective of this study was to evaluate and compare tetrahedral and hexahedral finite element meshes of simplified and realistic proximal intact femur geometries. Theoretical expressions of stresses and strains were derived for the simplified model of the femur. For the analysis of the realistic geometry of the proximal femur, a CAD model of the third generation composite femur (Pacific Research Labs, Vashion Island, WA) was used and simulations were performed with Hyperworks (Altair Engineering, Inc., Troy, MI) finite element analysis software. Convergence tests with hexahedral (8- and 20-node brick-elements) and tetrahedral (4- and 10-node tetrahedrons) elements were analysed by comparing the periosteal von Mises stresses and principal strains at a selected point of the femur. The numerical periosteal strains were also compared with experimental ones to determine the accuracy of the finite elements. Overall, we concluded, for the simplified femur, that tetrahedral linear element allowed results more closely to theoretical ones, but hexahedral quadratic elements seem to be more stable and less influenced to the degree of refinement (NDOF) of the mesh. It was not possible to correlate these findings with those observed for the realistic proximal femur simulations where no significant differences were seen using refined meshes, with more than NDOF=20,000 for hexahedral elements.

Algorithms↗

PubMed2006

Simulation of physiological loading in total hip replacements.

The determination of biomechanical force systems of implanted femurs to obtain adequate strain measurements has been neglected in many published studies. Due to geometric alterations induced by surgery and those inherent to the design of the prosthesis, the loading system changes because the lever arms are modified. This paper discusses the determination of adequate loading of the implanted femur based on the intact femur-loading configuration. Four reconstructions with Lubinus SPII, Charnley Roundback, Muller Straight and Stanmore prostheses were used in the study. Pseudophysiologic and nonphysiologic implanted system forces were generated and assessed with finite element analysis. Using an equilibrium system of forces composed by the Fx (medially direction) component of the hip contact force and the bending moments Mx (median plane) and My (coronal plane) allowed adequate, pseudo-physiological loading of the implanted femur. We suggest that at least the bending moment at the coronal plane must be restored in the implanted femur-loading configuration.

Computer Simulation↗

PubMed2006

Application of a vibration measuring technique to evaluate the dynamic stiffness of porcine periodontal ligament.

The performance of a tooth replacement by using a dental implant relies on the mechanical and biological capability of the anatomical substitute to restore lost physiological functions. The design of an implant device able to properly replace the physiological tooth requires the study of the load transfer mechanism at the implant-bone interface and the understanding of the relevance of the periodontal ligament (PDL) in this mechanism. The PDL is a connective soft tissue that provides the fixation of the tooth in its bone-socket and the attenuation of occlusal loads. It also provides the ground cells that are involved in the remodelling process, induced by a change in the stress-strain pattern of the alveolar bone and also in the cementum of the tooth root. The purpose of this study was to determine the PDL effects on the dynamic load transfer mechanism, from the tooth to the alveolar bone, evaluating the equivalent dynamic stiffness of the ligament structure. A porcine fresh mandible with a tooth was used within the study, applying an experimental procedure to identify the dynamic transmissibility of the entire system. The transmissibility function provided information about the stiffness and damping of the PDL, information that can assist the design of an improved dental implant system.

Alveolar Process↗

PubMed2004

Viscoelastic behaviour and failure of bovine cancellous bone under constant strain rate.

A programme has been established to characterize the long-term behaviour of cancellous bone. Fresh bovine cancellous specimens of dimensions 10 x 10 x 10 mm3 and 10 x 40 x 3.6 mm3 were manufactured and used within the testing programme. Results published in the literature indicate that the long-term behaviour of cancellous bone is well described by a power law, which is a very similar response of typical polymers. So far, dynamic mechanical tests (DMA) in three-point bending, under frequencies between 0.01 and 100 Hz at room temperature, confirmed the published results in a qualitative way. Nevertheless, the measured dimensionless damping, tan delta, was slightly higher than the values reported in the literature for the compact bone. The relaxation curves were obtained from dynamic tests and confirmed that bone relaxation modulus can be described by a power law function of time. Tests under constant compression strain rate were performed at four different strain rates: 0.15/s, 0.015/s, 0.0015/s and 0.00015/s and strain rate dependent behaviour was observed. An average elastic bending modulus of 300 MPa was obtained.

Animals↗

PubMed2002

The influence on strain shielding of material stiffness of press-fit femoral components.

The investigation and development of hip prostheses that can provoke identical strain patterns with those of the intact femur (physiological strains) are challenging design problems that have been addressed by several researchers. The modification of the physiological femoral strain pattern provokes adverse tissue biological reactions such as bone hypertrophy, as well as possible mechanical failure of the bone-implant construction. Investigators have used numerical and experimental methods to study the influence of the prosthesis material and geometry on physiological strain deviation. Within the present study, same geometry femoral components composed of different materials have been analysed using strain gauges. The effect of stem stiffness on the strain deviation relatively to those obtained with the intact femur was assessed. Five similar Freeman's prostheses made of different materials (steel, aluminium, composite and polyurethane) at the proximal and middle distal regions were manufactured and tested. The results revealed that only at the proximal lateral and proximal medial aspects of the femur were some differences observed between the strain patterns of the prostheses studied.

Elasticity↗

PubMed2001

Numerical-experimental method for the validation of a controlled stiffness femoral prosthesis.

The aim of this paper is to describe a new numerical-experimental method to determine the stiffness of a conceptual proximal femoral prototype. The methodology consists of the comparison of the numerical and experimental displacement distributions of the prosthesis loaded as a cantilever beam to validate a design concept: controlled stiffness prosthesis. The manufactured prototype used to test the applicability of the numerical-experimental procedure integrates a stiff metal core bonded to a composite material made of an epoxy resin reinforced with carbon-glass braided pre-forms. The prosthesis with an embedded controlled stiffness concept was obtained by varying the geometry of the core with the composite layer thickness.

Biomechanical Phenomena↗

PubMed2000

Influence of head constraint and muscle forces on the strain distribution within the intact femur.

The aim of this study was to analyse the influence of muscle action and a horizontally constrained femoral head on the strain distribution within the intact femur. The strain distribution was measured for three loading configurations: joint reaction force only, joint reaction force plus abductors, and joint reaction force plus the abductors, vastus lateralis and iliopsoas. In each case the strains were recorded from 20 uniaxial strain gauges placed on the medial, lateral, anterior and posterior aspects of the proximal femur. Application of the abductor muscle force produced a marginal decrease in the strain levels on all aspects of the femur as compared with the joint reaction force alone. This is in contrast with previous studies which have simulated an unconstrained femoral head. The inclusion of vastus lateralis and iliopsoas further reduced the strain levels. A horizontally constrained femoral head produces smaller variation in the strain levels when muscle forces are applied. In vivo data, demonstrating negligible movement of the femoral head in one-legged stance, support the results of this study and suggest that in the absence of comprehensive muscle force data, a constrained femoral head may provide a more physiologically relevant loading condition.

Elasticity↗

PubMed2000

Prevalence of cardiovascular risk factors in a rural population between 25 and 44 years old.

OBJECTIVES: The objective of this study was to evaluate the prevalence of the following cardiovascular risk factors, in the 25 to the 44 year age group, in persons attending the Goes Health Center: hypertension, high blood cholesterol, obesity, smoking and family history of coronary disease. METHODS: 340 individuals were selected, for random sample stratification by sex and age groups. They were summoned by mail to come to the Health Center for an evaluation of the factors studied. Hypertension was defined if systolic blood pressure was > or = 140 mmHg and/or diastolic arterial pressure was > or = 90 mmHg and/or if the participant was currently under therapy. High blood cholesterol was defined if the determination made at the time with a strip-test "Accutrend Cholesterol" was > or = 200 mg/dl and/or under specific therapy. Obesity was defined as a body mass index > or = 30 kg/m2. Tobacco consumption was defined as an affirmative reply to the question "Do you currently smoke?". Previous family history of coronary heart disease was defined as an affirmative reply to the question "Do you know of anybody in your family who has died or suffers from coronary disease?". RESULTS: The global prevalence of hypertension, high blood cholesterol, obesity, smoking and previous family history of coronary heart disease was of 20.3%, 32.1%, 11.8%, 21.5% and 26.8%, respectively. There was an association of risk factors in 22.3%.

Adult↗

PubMed1999

Circulating heat shock proteins in women with a history of recurrent vulvovaginitis.

OBJECTIVE: Predisposing factors influencing recurrences of bacterial vaginosis (BV) or vaginitis from Candida remain unidentified for most women. As a component of studies to determine host susceptibility factors to genital tract infections in women, we measured expression of the 60-kDa and 70-kDa heat shock proteins (hsp60 and hsp70, respectively) in the circulation of women with or without a history of recurrent BV or candidal vaginitis and with or without a current lower genital tract infection. Heat shock protein expression is associated with a down-regulation of pro-inflammatory immune responses that would inhibit microbial infection. METHOD: The investigators measured hsp60 and hsp70, antibodies to these proteins, the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha), and the anti-inflammatory cytokine interleukin-10 (IL-10) in sera by ELISA. The study population consisted of 100 women who attended a gynecology clinic in Campinas, Brazil. Of those, 55 had a history of recurrent vulvovaginitis (RV), while 45 were controls with no such history. Only women who were asymptomatic for at least 1 month were studied. RESULTS: Although all were asymptomatic, clinical and microbiological examination revealed that five of the women with a history of RV and two controls had a current candidal vaginal infection; 16 RV patients and 12 controls had BV; and six RV patients had both BV and candidiasis. Twenty-eight RV patients and 31 controls had no clinical or microbiological detectable vaginal infection. Among the RV patients, hsp60 and hsp70 were more prevalent in those with current BV (40.9% and 50.0%, respectively) or a candidal infection (45.5% and 54.5%) than in women with no current infection (21.4% and 17.9%). In the women with no history of RV, BV was not associated with a high prevalence of hsp60 (8.3%) or hsp70 (8.3%). Interleukin-10 and TNF were not more prevalent in vaginitis patients or controls with a current candidal infection or BV than in uninfected subjects. CONCLUSION: The high prevalence of circulating hsp60 and hsp70 in women with a history of RV and current BV or vaginal candidiasis, but not in women with no history of RV, suggests that differences in heat shock protein induction may be related to susceptibility to recurrent vaginal infections.

Adult↗

PubMed1999

Vaginal heat shock protein expression in symptom-free women with a history of recurrent vulvovaginitis.

OBJECTIVES: The cause of recurrent vulvovaginitis remains unexplained in most cases. Heat shock protein synthesis is induced under conditions of stress; its presence in vaginal samples from women who were between episodes of recurrent vulvovaginitis thus might reflect a persistent perturbation in the local milieu. STUDY DESIGN: We undertook an evaluation by means of enzyme-linked immunosorbent assay of 60-kd heat shock protein and inducible 70-kd heat shock protein expressions in vaginal wash samples from 24 symptom-free women with a history of recurrent vulvovaginitis and 19 matched control subjects. The samples were also tested for Candida albicans, Chlamydia trachomatis, Ureaplasma urealyticum, Mycoplasma hominis, and human papillomavirus by polymerase chain reaction; for bacterial vaginosis by clinical and microbiologic evaluation; and for interleukin 10, interleukin 1, interleukin 8, RANTES, and eotaxin by enzyme-linked immunosorbent assay. RESULTS: The presence of 60-kd heat shock protein was detected in 11 women with recurrent vulvovaginitis (45.8%) and 1 control subject (5.3%, P =.005). Similarly, 70-kd heat shock protein was present in 8 patients with recurrent vulvovaginitis (33.3%) and no control subjects (P =.005). The presence of 60-kd heat shock protein and the presence of 70-kd heat shock protein were correlated with each other (P =.02), as were both 60-kd heat shock protein (P =.006) and 70-kd heat shock protein (P =.01) correlated with IL-10. There was no relation between the presence of 60-kd heat shock protein or 70-kd heat shock protein and detection of IL-1, IL-8, or any microorganism. CONCLUSION: The expression of heat shock proteins and IL-10 in the vaginas of women with a history of recurrent vulvovaginitis but not in the vaginas of control subjects suggests the existence of differences in the vaginal milieu between the 2 groups, even when both are without vaginal symptoms.

Adult↗

PubMed1998

Prevalence of cervicovaginal infections during gestation and accuracy of clinical diagnosis.

OBJECTIVES: The aim of this study was to establish the prevalence of cervicovaginal infections in normal third-trimester pregnant women and evaluate the accuracy of clinical diagnosis. METHOD: A total of 328 pregnant women were followed at the Prenatal Outpatient Clinic of the Department of Obstetrics and Gynecology at the School of Medical Sciences, Universidade Estadual de Campinas (UNICAMP), Brazil, from October 1991 to February 1993. The clinical diagnosis was based on the characteristics of the vaginal discharge, and the etiological diagnosis was based on bacterioscopy of the vaginal secretion and direct immunofluorescence for Chlamydia trachomatis. The data were analyzed statistically, determining the sensitivity, specificity, and positive and negative predictive value of the clinical diagnosis related to the laboratory diagnosis of the different infections. RESULTS: The prevalence of infection was 39.6% (Candida albicans, 19.2%; bacterial vaginosis, 9.5%; intermediate vaginal flora, 6.7%; Chlamydia trachomatis, 2.1%; and vaginal trichomoniasis, 2.1%). The accuracy of clinical diagnosis was low, with sensitivity between 50% and 65% and specificity around 60%, with the exception of trichomoniasis, which showed a sensitivity of 100% and chlamydia, with a sensitivity of 0% and a specificity of 100%. CONCLUSION: The accuracy of the clinical diagnosis of infections was low, specifically with respect to the positive predictive value. The results demonstrate the need for specific testing of cervicovaginal infections at prenatal visits. Reliance on simple vaginal examination results in a low yield for detection of vaginal infections.

Adolescent↗

PubMed1998

Preliminary investigation of a novel controlled stiffness proximal femoral prosthesis.

Previous studies have suggested that a controlled stiffness prosthesis is required to address the conflicting requirements of minimizing stress shielding and micromotion. The design for a controlled stiffness prosthesis is proposed and a preliminary analytical investigation performed to assess its predicted performance before fabrication of a prototype component. The novel prosthesis consisted of a cobalt-chrome core and a flexible composite outer layer. Varying the composite layer thickness allowed the prosthesis stiffness to be controlled. Three variants of the controlled stiffness prosthesis were critically assessed using the finite element method and their predicted performance compared with those of conventional prosthesis designs. The potential for stress shielding was assessed by examining the periosteal strain energy and the potential for migration assessed by examining the endosteal minimum principal cancellous bone stresses. Both the conventional and controlled stiffness implants performed poorly as press-fit prostheses. All the press-fit prostheses generated high cancellous bone stresses, suggesting that excessive migration of these implants would be likely. The controlled stiffness implants performed better than the conventional implants when bonded to the surrounding bone. Although the controlled stiffness implants did not eliminate stress shielding of the calcar, they produced higher strain energies than the conventional designs. The findings of this study are that osseointegrated controlled stiffness implants may perform better than current osseointegrated cementless prostheses and therefore it is worth while progressing to the next stage, of prototyping an implant.

Biocompatible Materials↗