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Biomedical subjects

M J Fagan

Publications and source records attributed to M J Fagan.

At least 19 recordsLinked to original sources
PubMed2007

Assessing mechanical function of the zygomatic region in macaques: validation and sensitivity testing of finite element models.

Crucial to the interpretation of the results of any finite element analysis of a skeletal system is a test of the validity of the results and an assessment of the sensitivity of the model parameters. We have therefore developed finite element models of two crania of Macaca fascicularis and investigated their sensitivity to variations in bone material properties, the zygomatico-temporal suture and the loading regimen applied to the zygomatic arch. Maximum principal strains were validated against data derived from ex vivo strain gauge experiments using non-physiological loads applied to the macaque zygomatic arch. Elastic properties of the zygomatic arch bone and the zygomatico-temporal suture obtained by nanoindentation resulted in a high degree of congruence between experimental and simulated strains. The findings also indicated that the presence of a zygomatico-temporal suture in the model produced strains more similar to experimental values than a completely separated or fused arch. Strains were distinctly higher when the load was applied through the modelled superficial masseter compared with loading an array of nodes on the arch. This study demonstrates the importance of the accurate selection of the material properties involved in predicting strains in a finite element model. Furthermore, our findings strongly highlight the influence of the presence of craniofacial sutures on strains experienced in the face. This has implications when investigating craniofacial growth and masticatory function but should generally be taken into account in functional analyses of the craniofacial system of both extant and extinct species.

Animals↗
PubMed2006

Three dimensional stereolithography models of cancellous bone structures from muCT data: testing and validation of finite element results.

Stereolithography (STL) models of complex cancellous bone structures have been produced from three-dimensional micro-computed tomography data sets of human cancellous bone histological samples from four skeletal sites. The STL models have been mechanically tested and the derived stiffness compared with that predicted by finite element analysis. The results show a strong correlation (R2 = 0.941) between the predicted and calculated stiffnesses of the structures and show promise for the use of STL as an additional technique to complement the use of finite element models, for the assessment of the mechanical properties of complex cancellous bone structures.

Biomimetics↗
PubMed2004

A comparative study of aortic wall stress using finite element analysis for ruptured and non-ruptured abdominal aortic aneurysms.

BACKGROUND: The decision to repair an asymptomatic abdominal aortic aneurysm (AAA) is currently based on diameter (> or =5.5 cm) alone. However, aneurysms less than 5.5 cm do rupture while some reach greater than 5.5 cm without rupturing. Hence the need to predict the risk of rupture on an individual patient basis is important. This study aims to calculate and compare wall stress in ruptured and non-ruptured AAA. METHODS: The 3D geometries of AAA were derived from CT scans of 27 patients (12 ruptured and 15 non-ruptured). AAA geometry, systolic blood pressure and literature derived material properties, were utilised to calculate wall stress for individual AAA using finite element analysis. RESULTS: Peak wall stress was significantly higher in the ruptured AAA (mean 1.02 MPa) than the non-ruptured AAA (mean 0.62 MPa). In patients with an identifiable site of rupture on CT scan, the area of peak wall stress correlated with rupture site. CONCLUSIONS: Peak wall stress can be calculated from routinely performed CT scans and may be a better predictor of risk of rupture than AAA diameter on an individual patient basis.

Aged↗
PubMed2003

Cutting or round-bodied needles for tendon repair.

We carried out a biomechanical study comparing tensile strength after using round-bodied or cutting needles for tendon repair. Swine tendons were repaired in three groups: Group 1 core suture repair only; group 2 core and circumferential suture repair; and group 3 isolated circumferential suture repair. The tendons were tested at longitudinal stress to failure at 5mm/minute. No significant differences were found between the round-bodied and cutting needles in any group. Equal numbers in the core suture repair group failed by suture pullout when comparing cutting and round-bodied needles. We conclude that the choice of needle has no effect on the outcome of tendon repair if there is consistency of surgeon's skill and experience.

Animals↗
PubMed2003

Stereo visualization of 3D trabecular bone structures produced by bone remodelling simulation.

Adult human bone is constantly being renewed by a process known as remodelling. For cancellous bone this renewal process occurs at the interface between bone and marrow where bone is depleted by osteoclasts and rebuilt by osteoblasts. This remodelling process allows bone to repair itself. Software simulators for bone remodelling provide insight into the bone remodelling process; they allow investigation into bone form and structural properties, and they also allow the emulation of bone diseases and possible treatments for these diseases over long periods of time. BONESIM is a software that simulates bone remodelling in terms of Basic Multi-cellular Units (BMUs). 3D visualization of trabecular bone and its attributes is an essential tool in understanding this remodelling process for cancellous bone. It enables the bone researcher to quickly understand the dynamic behaviour of remodelling, the resulting geometry of the bone structure and it allows alternative remodelling scenarios to be compared. This paper presents the volume visualization technique that has been developed to provide this visualization tool.

Adult↗
PubMed2002

Finite element analysis in spine research.

Finite element analysis is a widely accepted tool used in many industries and research activities. It allows new designs to be thoroughly 'tested' before a prototype is even manufactured, components and systems which cannot readily be experimented upon to be examined, and 'diagnostic' investigations to be undertaken. Finite element models are already making an important contribution to our understanding of the spine and its components. Models are being used to reveal the biomechanical function of the spine and its behaviour when healthy, diseased or damaged. They are also providing support in the design and application of spinal instrumentation. The spine is a very complex structure, and many of the models are simplified and idealized because of the complexity and uncertainty in the geometry, material properties and boundary conditions of these problems. This type of modelling simplification is not peculiar to spinal modelling problems. Indeed, the idealization is often a strength when there is such uncertainty and variation between one individual and another, allowing cause-effect relationships to be isolated and fully explored, and the inherent variability of experimental tests to be eliminated. This paper reviews the development of finite element analysis in spinal modelling. It shows how modelling provides a wealth of information on our physiological performance, reduces our dependence on animal and cadaveric experiments and is an invaluable complement to clinical studies. It also leads to the conclusion that, as computing power and software capabilities increase, it is quite conceivable that in the future it will be possible to generate patient-specific models that could be used for patient assessment and even pre- and inter-operative planning.

Biomechanical Phenomena↗
PubMed2002

Patient-specific spine models. Part 1: Finite element analysis of the lumbar intervertebral disc--a material sensitivity study.

If patient-specific finite element models of the spine could be developed, they would offer enormous opportunities in the diagnosis and management of back problems. Several generic models have been developed in the past, but there has been very little detailed examination of the sensitivity of these models' characteristics to the input parameters. This relationship must be thoroughly understood if representative patient-specific models are to be realized and used with confidence. In particular, the performance of the intervertebral discs are central to any spine model and need detailed investigation first. A generic non-linear model of an intervertebral disc was developed and subjected to compressive, flexion and torsional loading regimes. The effects of both material and geometric non-linearities were investigated for the three loading schemes and the results compared with experimental data. The basic material properties of the fibres, annulus and nucleus were then varied and the effects on the stiffness, annulus bulge and annulus stresses analysed. The results showed that the non-linear geometry assumption had a significant effect on the compression characteristics, whereas the non-linear material option did not. In contrast, the material non-linearity was more important for the flexural and torsional loading schemes. Thus, the inclusion of non-linear material and geometry analysis options in finite element models of intervertebral discs is necessary to predict in vivo load-deflection characteristics accurately. When the influence of the material properties was examined in detail, it was found that the fibre properties did not have a significant effect on the compressive stiffness of the disc but did affect the flexural and torsional stiffnesses by up to +/-20 per cent. All loading modes were sensitive to the annulus properties with stiffnesses varying by up to +/-16 per cent. The model also revealed that for a particular compressive deformation or flexural or torsional rotation, the disc bulge was not sensitive to any of the material properties over the range of properties considered. The annulus stresses did differ significantly as the material properties were varied (up to 70 per cent under a compressive load and 60 per cent during disc flexion).

Compressive Strength↗
PubMed2000

Stochastically simulated assessment of anabolic treatment following varying degrees of cancellous bone resorption.

The aim of this study was to investigate the recovery in cancellous bone stiffness resulting from anabolic treatment following varying degrees of resorption, using a stochastic simulation applied to a simplistic structure consisting of five vertical and five horizontal trabeculae. The structure was initially resorbed, and "bone" elements were stochastically removed until nominal resorptions of 10%, 15%, 20%, 25%, and 30% were achieved. A stochastic simulation of anabolic treatment was then applied where bone elements were added, continuing until the original stiffness had been regained, for example, simulating treatment of a patient with an anabolic agent after a period of postmenopausal resorption. The resorption and anabolic simulations were repeated three times for each of the nominal resorptions. The stiffness of the bone structure decreased linearly with resorption, with a slope of approximately -2 and an R(2) of 97.0%; hence, the stiffness fell at approximately twice the rate of the reduction in density. When the various structures regained their original density, the resultant stiffness also had a linear relationship with the original resorption, with a slope of -1 and a lower R(2) of 86.1%. This implies that the reduction in stiffness, when original density was regained, fell proportionately with the degree of initial resorption and, therefore, after a resorption of 30%, when original density was regained, the stiffness of the resultant structure was approximately 30% less than that of the original structure. The density required for the original stiffness to be regained increased linearly with the degree of initial resorption, with a slope of approximately 0.5 and an R(2) of 65.2%, lower than that observed for the previous relationships. This indicates a greater spread of data and suggests greater variability in the formation phase beyond the point of regained original density. Because irreversible connectivity reduction is widely considered to be one of the earliest manifestations of estrogen loss, these findings, although obtained on a simulation of a simplistic cancellous bone structure, support the concept of early intervention to prevent potentially irreversible deterioration of trabecular architecture after menopause.

Bone Resorption↗
PubMed1999

Satisfaction with methods of Spanish interpretation in an ambulatory care clinic.

OBJECTIVE: To describe the utilization of various methods of language interpretation by Spanish-speaking patients in an academic medical clinic and to determine patients' and physicians' satisfaction with these methods. METHODS: Survey administered to medical residents and Spanish-speaking patients asking about their experience and satisfaction with various methods of language interpretation. MAIN RESULTS: Both patients and residents had the highest level of satisfaction for professional interpreters (92.4% vs 96.1% reporting somewhat or very satisfactory, p =.17). In contrast, patients were significantly more satisfied than residents with using family members and friends (85.1% vs 60.8%, p <.01). Physicians and patients agreed that accuracy, accessibility, and respect for confidentiality were highly important characteristics of interpreters (>90% of both groups reporting somewhat or very important). However, patients were more concerned than residents about the ability of the interpreter to assist them after the physician visit (94% vs 45.1%, p < 0.01). CONCLUSIONS: Using family members and friends as interpreters for Spanish-speaking patients should be more seriously considered; however, in order to optimize patient satisfaction, differences between patients and providers should be taken into account when using interpretation in medical settings.

Ambulatory Care Facilities↗
PubMed1999

Enhanced emergency department referral improves primary care access.

OBJECTIVE: People who use the emergency department (ED) as their main source of medical care cite access barriers to primary care as the reason. The purpose of this study was to test an intervention designed to refer regular ED users to primary care. STUDY DESIGN: A prospective randomized clinical trial. PATIENTS AND METHODS: Adults who stated the ED is their regular source of care and have no primary care (n = 189) were randomized to 2 groups: the intervention being studied or usual care. The study took place over 3 months at a northeastern urban hospital. RESULTS: Subjects in the intervention group were more than twice as likely to keep the primary care appointment compared with the usual care group, and most also received some measure of preventive care. There was no significant difference in ED utilization by these patients in the 12-month period following study entry. CONCLUSION: Making an appointment with detailed instructions during a visit to the ED markedly improves show rates at follow-up appointments with a primary care provider and allowed for opportunity to provide important preventive services.

Adult↗
PubMed1999

Use of an open-ended question to supplement a patient satisfaction questionnaire in a medical residents' clinic.

OBJECTIVES: To determine (1) the proportion of responses to an open-ended question related to patient satisfaction that could be categorized into 1 or more of 9 previously developed domains of out-patient care and (2) whether any other important aspects of care could be identified by adding the open-ended question to a satisfaction questionnaire. STUDY DESIGN: A 3-month observational study was done at the internal medicine clinic of an urban teaching hospital. PATIENTS AND METHODS: As part of a patient satisfaction study, 511 visitors were asked after their visit, "What are the 1 or 2 things that are most important to you when you see a doctor?" The responses were categorized independently by 2 raters into 1 or more of the 9 domains. When these 2 raters disagreed, the responses were read to a third rater. When either all 3 raters disagreed, or at least 1 rater thought a new domain was mentioned, those responses were categorized by consensus. Interobserver reliability between raters 1 and 2 was calculated by using Cohen's kappa statistic. RESULTS: The 355 responses were categorized as follows: 303 (85.4%) identified one or more domains that were part of the previously developed taxonomy, 9 (2.5%) identified a new domain, 11 (3.1%) identified both old and new domains, and 32 (9.0%) could not be categorized. Cohen's kappa was 0.57 (P < .001). Cultural sensitivity and physician honesty were the additional domains identified, by 1.1% and 4.5% of respondents, respectively. CONCLUSIONS: The previously developed taxonomy of domains can be used in this setting to categorize the large majority of open-ended responses. Such responses can identify important aspects of care that were either previously unidentified or were already identified but given low ratings. This information then can help improve quality of care.

Adult↗
PubMed1998

Dynamic stochastic simulation of cancellous bone resorption.

A stochastic simulation of cancellous bone resorption was developed and applied to a simple two-dimensional lattice structure representing the vertebral body. The simulation is based upon the concept of a basic multicellular unit (BMU) where net resorption (-deltaB.BMU) is considered at bone/marrow surfaces. The cancellous bone structure is defined as a binary matrix with the size of the pixels corresponding to a square element of approximately 20 microm dimension. The simulation considers both the probability that any surface pixel will be activated into a BMU and, if activated, the length of the resorption cavity. The relationship between relative stiffness and density for the simulation was predicted by finite element analysis. The stochastic simulation was iterated eight times with the mechanical properties assessed after each stage. Perforation of a single trabeculae was first observed at step 2, the structure completely lacking connectivity and mechanical integrity by step 8. The slope of the stiffness-porosity graph was greater than unity for the first five steps, but thereafter approached zero because the structure had lost connectivity and effectively collapsed. The eight-step simulation was repeated five times and demonstrated that, although the stiffness/density relationships were similar at the extremes of density, the dependence of stiffness upon density varied. This clearly demonstrates the stochastic nature of the simulation upon cancellous bone structure, and is probably indicative of a significant dependence of mechanical integrity upon perforation effects.

Biomechanical Phenomena↗
PubMed1997

Do internists and emergency physicians agree on the appropriateness of emergency department visits?

The purpose of this study was to determine the levels of agreement between three methods of assessing appropriateness of emergency department (ED) visits. In particular, we tested the agreement between internists and emergency physicians reviewing the ED nurses' triage notes, containing information that might be available by telephone to an internist. For 892 adult patient ED visits reviewed, we found only moderate agreement (kappa = 0.47) between these groups. In cases of disagreement, emergency physicians were 10.3 times more likely than internists to classify those with minor discharge diagnoses as appropriate for ED care. As managed care grows, the determination of ED appropriateness may depend on open discussions between physician groups, as well as on access to timely care in office settings.

Adult↗
PubMed1997

The effect of primary care training on patient satisfaction ratings.

This study examines the association between type of internal medicine training and satisfaction ratings among 509 patients who visited the clinic of an urban teaching hospital over a 3-month period in 1994. When controlling for patient, health-system, and other resident factors, primary care training was significantly associated with higher satisfaction ratings (cumulative odds ratio 1.53; 95% confidence interval 1.04, 2.25; p = .031) than categorical training. Using satisfaction ratings to rank the residents without adjusting for patient and health-system factors would have correctly classified only 27% of the residents in the lowest quartile. These findings have implications for both the education and potential employment of internists.

Adolescent↗