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Biomedical subjects

J P Paul

Publications and source records attributed to J P Paul.

At least 19 recordsLinked to original sources
PubMed2003

Direct comparison of calculated hip joint contact forces with those measured using instrumented implants. An evaluation of a three-dimensional mathematical model of the lower limb.

Characterisation of hip joint contact forces is essential for the definition of hip joint prosthesis design requirements. In vivo hip joint contact force measurements have been made using instrumented hip joint prostheses. However, to allow determination of the range of values of joint contact force and their directions relative to anatomical structures in a range of subject groups sufficient to form an agreed data base it is necessary to adopt a different approach without the use of an implanted transducer. The use of mathematical models of the lower limb to examine the forces in soft tissues and at the joints has provided valuable insight into internal loading conditions. Several authors have proposed mathematical musculo-skeletal models. However, there have been only limited attempts at validation of these models. It is possible to use the results of in vivo force measurements from instrumented prostheses to validate the results calculated using the mathematical models. In this study two subjects with instrumented hip joint prostheses were studied. Forces at the hip joints were calculated using a three-dimensional model of the leg. Walking at slow, normal and fast speeds (0.97-2.01m/s), weight transfer from two to one leg and back again, and sit to stand were studied. Direct comparisons were made between the 'gold standard' measured hip joint contact forces and the calculated forces. There was general agreement between the calculated and measured forces in both pattern and magnitude. There were, however, discrepancies. Reasons for these differences in results are discussed and possible model developments suggested.

Computer Simulation↗
PubMed2001

National trends in condom use among at-risk heterosexuals in the united states.

Based on national level surveys, we examined data relevant to the United States' overall effort to prevent the spread of HIV among heterosexual adults. We examined changes in condom use among at-risk heterosexuals over the past decade. The observed increases over time in condom use across all heterosexual at-risk population segments are consistent with the observed (declines) trends in HIV and syphilis in the 1990s. These results and findings from prior studies suggest that U.S. efforts to facilitate condom use and contain HIV and related sexually transmitted disease (STD)-cofactors among adult at risk heterosexuals was succeeding over most of the 1990s. The absence of national level behavioral trend data after 1996, and the ambiguities of HIV spread suggest some caution in projecting trends into this century. National and local efforts need to be directed at sustaining behavioral change and conducting more rigorous studies on population trends in HIV/STD-related behaviors/pathogens.

Adolescent↗
PubMed2001

Experimental investigation of failure load and fracture patterns of C2 (axis).

The injury mechanism and magnitude of failure load of C2 fractures are important in the clinical treatment of its fixation. The magnitudes of the failure load of C2 and the mechanism of injury in vivo are uncertain. Accordingly, nine C2 vertebrae obtained from cadaver spines, ranging in age from 51 to 80 years, were used for the study. Special restraint conditions were applied to yield specific fracture of C2. With the posterior element potted postero-anteriorly up to one-quarter of the inferior facet, posterior shear force ranging from 840 to 1220N was required to cause fracture across the pars interarticularis. For odontoid fracture study, a special rig was fabricated to encapsulate the body of C2 in a cell using ISOPON, and a thin layer of ISOPON sandwiched between the inferior facets and two lateral plates. The assembled rig permits slight sagittal movement of C2 about the cup lateral pivot supports. Failure load of between 900 and 1500N was recorded for odontoid fracture. These values are in agreement with published data. The experiment carried out under these two different restraint conditions had specifically resulted in different fractures of C2. In reality, depending on factors such as the inclination of this force vector applied to the head, the precise posture at the time of trauma, the spinal geometry, and the physical properties, different types of fracture patterns of C2 may be produced. This additional data will be useful in the biomechanical study of C2 vertebra using analytical approaches, and in surgical anterior/posterior fixation using screws.

Aged↗
PubMed2001

Understanding childhood sexual abuse as a predictor of sexual risk-taking among men who have sex with men: The Urban Men's Health Study.

OBJECTIVE: The prevalence and characteristics of childhood sexual abuse (CSA) among men who have sex with men (MSM), and links with sexual risk are explored. A model linking CSA and sexual risk among MSM is proposed. METHOD: A telephone probability sample of urban MSM (n = 2881) was recruited and interviewed between November 1996 and February 1998. The interview covered numerous health issues, including history of sexual victimization. RESULTS: One-fifth reported CSA, primarily by non-family perpetrators. Initial CSA experiences are characterized by high levels of force (43% involved physical force/weapons), and penetrative sex (78%; 46% reported attempted or actual anal intercourse). Such men are more likely than nevercoerced men to engage in high risk sex (unprotected anal intercourse with a non-primary partner or with a serodiscordant male). In multivariate analyses, the effect of childhood sexual coercion on sexual risk is mediated by substance use, patterns of sexual contacts, and partner violence, but not by adult sexual revictimization or by depression. CONCLUSIONS: Findings are interpreted within the context of social learning theory and prior research on sexual risk-taking. The high risk for CSA among MSM, which can predispose such men to patterns of HIV sexual risk, warrants new approaches in HIV prevention.

Adolescent↗
PubMed2001

Alcohol use, drug use and alcohol-related problems among men who have sex with men: the Urban Men's Health Study.

AIMS: To measure the prevalence and independent associations of heavy and problematic use of alcohol and recreational drugs among a household-based sample of urban MSM (men who have sex with men). DESIGN: Cross-sectional survey. PARTICIPANTS: Men who identified as being gay or bisexual or who reported sex with another man in the prior 5 years were included in this analysis (n = 2172). SETTING: A probability telephone sample of MSM was taken within Zip Codes of four large American cities (Chicago, Los Angeles, New York and San Francisco) estimated to have total concentrations of at least 4% of all households with one resident MSM. MEASUREMENTS: Standard measures of alcohol use, problems associated with alcohol use, and recreational drug use were administered by trained telephone interviewers. FINDINGS: Both recreational drug (52%) and alcohol use (85%) were highly prevalent among urban MSM, while current levels of multiple drug use (18%), three or more alcohol-related problems (12%), frequent drug use (19%) and heavy-frequent alcohol use (8%) were not uncommon. The associations of heavy and/or problematic substance use are complex, with independent multivariate associations found at the levels of demographics, adverse early life circumstances, current mental health status, social and sexual practices and connection to gay male culture. CONCLUSIONS: The complex pattern of associations with heavy and/or problematic substance use among urban MSM suggests that heavy and/or problematic substance use is grounded in multiple levels: the individual, the interpersonal and the socio-cultural.

Adolescent↗
PubMed2001

The effect of heel elevation on strain within the plantar aponeurosis: in vitro study.

Mild, temporary reduction of symptoms from plantar fasciitis have been reported with the use of high heeled shoes (i.e. cowboy boots, ladies pumps). However, little is known on how heel elevation may contribute to a decrease in the pain and inflammation. The aim of this study was to quantify strain in the plantar aponeurosis in cadaveric feet with the use of various heel elevation configurations. An in vitro method that simulated "static" stance was used to determine the loading characteristics of the plantar aponeurosis (n = 12). Heel elevation was evaluated with blocks placed beneath the heel and with a contoured platform that simulated the arch profile of a shoe at three different heel heights (2.0, 4.0, 6.0 cm) with a level plane serving as the control. Strain in the plantar aponeurosis decreased with elevations of the heel that simulated the arch profile of a shoe at load levels (337, 450 N) (P < 0.05). Elevations of the heel with blocks did not significantly affect strain in the plantar aponeurosis (P < 0.05). Contrasting results of some specimen limbs compared with the overall means suggests that the influence of heel elevation on loading of the plantar aponeurosis may be dependent on individual variation and foot structure differences. Therefore, clinicians should be cautious in recommending heel elevation as a treatment for plantar fasciitis since some subjects may not achieve the desired decrease in plantar aponeurosis strain.

Adult↗
PubMed2001

The continuing HIV epidemic among men who have sex with men.

OBJECTIVES: This study characterized the AIDS epidemic among urban men who have sex with men (MSM). METHODS: A probability sample of MSM was obtained in 1997 (n = 2881; 18 years and older) from New York, Los Angeles, Chicago, and San Francisco, and HIV status was determined through self-report and biological measures. RESULTS: HIV prevalence was 17% (95% confidence interval = 15%, 19%) overall, with extremely high levels in African Americans (29%), MSM who used injection drugs (40%), "ultraheavy" noninjection drug users (32%), and less educated men (< high school, 37%). City-level HIV differences were non-significant once these other factors were controlled for. In comparing the present findings with historical data based on public records and modeling, HIV prevalence appears to have declined as a result of high mortality (69%) and stable, but high, incidence rates (1%-2%). CONCLUSIONS: Although the findings suggest that HIV prevalence has declined significantly from the mid-1980s, current levels among urban MSM in the United States approximate those of sub-Saharan countries (e.g., 14%-25%) and are extremely high in many population subsegments. Despite years of progress, the AIDS epidemic continues unabated among subsegments of the MSM community.

Adolescent↗
PubMed2001

Health-related characteristics of men who have sex with men: a comparison of those living in "gay ghettos" with those living elsewhere.

OBJECTIVES: This study investigated the limitations of probability samples of men who have sex with men (MSM), limited to single cities and to the areas of highest concentrations of MSM ("gay ghettos"). METHODS: A probability sample of 2881 MSM in 4 American cities completed interviews by telephone. RESULTS: MSM who resided in ghettos differed from other MSM, although in different ways in each city. Non-ghetto-dwelling MSM were less involved in the gay and lesbian community. They were also less likely to have only male sexual partners, to identify as gay, and to have been tested for HIV. CONCLUSIONS: These differences between MSM who live in gay ghettos and those who live elsewhere have clear implications for HIV prevention efforts and health care planning.

AIDS Serodiagnosis↗
PubMed2001

Biomechanical study of C2 (Axis) fracture: effect of restraint.

INTRODUCTION: In human, the cervical spine region is very susceptible to impact injury. The complex structures of C1 and C2 serve to transmit the weight of the cranium to the greatly similar structural cervical spine from C3 caudally. Application of sudden disruption forces will detach the junction of the cervico-cranium with the pars interarticularis of the neural arch of C2 from the lower cervical spine by fracturing, as in a "hangman's fracture". Severe falls or blows to the head from heavy objects will cause the fracture of the odontoid process of C2. Many biomechanical studies were conducted based on full restraint of the inferior aspects of isolated C2 to produce odontoid fracture. In this study, two different restraining conditions of C2 were adopted experimentally to determine the absolute fracture load and the corresponding fracture patterns that are common to C2. MATERIALS AND METHODS: Nine C2 vertebrae obtained from cadaver spines, ranging from 51 to 80 years, were used. Two specified restraint conditions were employed: (1) fully constrain the posterior element postero-anteriorly up to one-quarter of the inferior facet; and (2) fixing of C2 by a specially-designed rig whereby the body of C2 embedded in the pivoted cup and its inferior facets positioned on top of two lateral plates. Antero-posterior shear force was applied on the anterior articulating facet of the dens until failure. RESULTS: These specified restraint conditions had resulted in specific fracture of C2. Antero-posterior shear force ranges from 840 to 1220 N was required to cause fracture across the pars interarticularis under restraint condition 1. Failure load of between 900 and 1500 N was found to cause odontoid fracture under restraint condition 2. These values are in agreement with published data. CONCLUSIONS: The biomechanical response of C2 was specific to the mode of restraint conditions of C2. In reality, depending on the force vector applied to the head, precise posture at the time of trauma, spinal geometry, and physical properties, different types of C2 fracture patterns may happen. These findings are of potentials for the biomechanical correlation and validation study of C2 vertebra using analytical approaches, and in the surgical anterior screw fixation of odontoid fracture.

Aged↗
PubMed2000

Determination of axial rotation angles of limb segments - a new method.

This paper describes a new method of determining the axial rotation angle of a limb segment during three-dimensional movement. Instead of describing the three-dimensional rotation by a three-step rotation (Euler/Cardan angles), a one-step rotation (instantaneous screw axis), or a non-step rotation (floating axis method), the new method uses a two-step rotation to describe the three-dimensional rotation of the limb segment: the rotation of the long axis of the limb segment about a specific axis passing through the proximal joint centre and perpendicular to the long axis of the limb segment, and the axial rotation about the long axis. A short review of previous methods followed by a full description of the principle of the new method with detailed derivation of some important equations (Appendices), comparison with Euler/Cardan angles and a simple experimental demonstration are given in this paper. A method of solving the gimbal-lock problem when using this method is also proposed.

Biomechanical Phenomena↗
PubMed2000

In vivo human tendinous tissue stretch upon maximum muscle force generation.

In the present study, we examined the hypothesis that stretch of tendinous tissue in the human tibialis anterior (TA) muscle-tendon unit upon isometric dorsiflexion maximum voluntary contraction (MVC) varies along the entire tendinous component length. Ultrasound-based measurements of the excursions of the TA tendon origin and proximal end of the TA central aponeurosis were taken in the transition from rest to MVC in six men. Subtracting the TA tendon origin excursion from the excursion of the aponeurosis proximal end, the aponeurosis excursion was estimated. Estimation of the aponeurosis proximal region excursion was obtained subtracting the excursion of the insertion point of a central region fascicle on the aponeurosis from the whole aponeurosis excursion. Subtracting tendon excursion from the excursion of the central fascicle insertion point, the aponeurosis distal region excursion was estimated. Strain values were calculated dividing the excursions obtained by the original resting lengths. All excursions and lengths were measured in the mid-longitudinal axis of the TA muscle-tendon unit at the neutral anatomical ankle position. Tendon excursion and strain were 0.5+/-0. 08 cm (mean+/-SE) and 3.1+/-0.2%, respectively. Aponeurosis excursion and strain were 1.1+/-0.15 cm and 6.5+/-0.6%, respectively. Aponeurosis distal region excursion and strain were 0.3+/-0.05 cm and 3.5+/-0.3%, respectively. Aponeurosis proximal region excursion and strain were 0.8+/-0.12 cm and 9.2+/-1%, respectively. Aponeurosis excursion and strain were larger by 110-120% (P<0.05) compared with tendon. Aponeurosis proximal region excursion and strain were larger by 165-170% (P<0.05) compared with aponeurosis distal region. These findings are in line with results from in vitro animal material testing and have important implications for theoretical models of muscle function.

Adult↗