Biomedical subjects
Publications and source records attributed to J P Paul.
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A knee simulating machine is required for the design and evaluation of total knee replacements, the kinematics and the long-term wear being aspects of particular importance. There are no generally agreed design criteria, such that existing designs of simulator have a wide variety of input and constraint conditions. In this study, it was postulated that in order to reproduce physiological wear patterns, the correct kinematics is required, on the basis that the wear will be a direct function of the sliding, rolling and tractive rolling conditions at the joint surfaces. In turn, the correct kinematics would only be achieved by the input of physiological forces, by the appropriate constraints on the fixtures holding the components, and by simulating the soft tissue restraints. A knee simulating machine based on these principles was constructed, and used to test the kinematics of a range of contemporary condylar replacement knees. The displacements and rotations varied over a range of almost two times, even with the soft tissue restraints. Without the restraints, the low constraint designs would have dislocated or moved unrealistically. It was concluded that a simulating machine should be based on the input of forces and moments, rather than on displacements and rotations, in order to provide data of kinematics and wear.
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A unilateral external fixator has been designed for controlled experiments into the effects of micromovement on fracture healing. The experimental model used is based on a diaphyseal osteotomy of the right tibia of the sheep. The main bar has linear bearings, which allows free axial movement. This is then controlled by a spring whose stiffness can be varied. The resulting axial micromovement can be calculated from the measured compressive force and the known axial stiffness of the fixator. The transducer has limits of error of +13.3 N and -44.5 N. Preliminary measurements showed maximum micromovement at the fracture site of 0.48 mm during slow walking.
In this study two aspects of hybrid functional electrical stimulation (FES) orthoses were investigated: joint motion constraints and FES control strategies. First, the effects of joint motion constraints on the gait of normal subjects were investigated using modern motion analysis systems, including electromyogram (EMG) and heart rate measurements. An orthosis was developed to impose joint motion constraints; the knee and ankle could be fixed or free, and the hip joint could rotate independently or coupled, according to a preset flexion-extension coupling ratio (FECR). Compared with a 1:1 hip FECR, a 2:1 hip FECR was associated with a reduced energy cost and increased speed and step length. The knee flexion during swing significantly reduced energy cost and increased walking speed. Ankle plantar flexion reduced the knee flexing moment during the early stance phase. Second, trials on 3 paraplegic subjects were conducted to implement some of these findings. It appeared that the 2:1 FECR encouraged hip flexion and made leg swing easier. A simple FES strategy increased walking speed and step length and reduced crutch force impulse using fixed orthotic joints.
Following work done in C.E.C. project AIM 2002 CAMARC II, a framework of the relevant standards for testing equipment used in laboratories analysing human movement is presented. In particular, gait analysis laboratories may provide a service for a clinical team considering treatment such as surgical intervention or provision of orthoses. In this case the analysis and equipment used in the analysis must have assured quality so that the correct clinical interpretation of the results is possible. The operation of a gait analysis laboratory may be described in quality standards terminology as the operation of a 'special process'. The operation of a special process requires that particular attention be paid to procedures including confirmation of the equipment and regular testing to ensure correct operation of the equipment. In general this is difficult to achieve since equipment manufacturers still have to address this technical requirement. Although difficult, these procedures must be accomplished in the operation of a special process. Passages of the most pertinent standards are presented and a methodology of a periodic confirmation and regular spot checking of equipment suggested to ensure its correct operation. Although force plates are specifically addressed, the framework could be applied to other dynamometers and measurement equipment.
This article reviews the need for standards for orthopaedic implants and illustrates the differences in approach of the European Standard Organization compared to National and International Standards. The areas where new work is being undertaken are outlined.
In this study the effects of angular motion constraints of the lower limbs on the gait of normal subjects were investigated. An assessment orthosis was developed with a new hip coupling mechanism which allows its ratio of reciprocal flexion to extension to be altered. The knee and ankle joints of the orthosis could also be set to be free or locked in specific directions of angular motion in the sagittal plane. A total of 12 different orthosis configurations was tested on three normal subjects. The kinematic, kinetic and electromyographic (EMG) data were collected using the VICON system, two Kistler forceplates, foot switches and an eight channel EMG system. The physiological cost index of walking was assessed by measuring the heart rate and walking speed. It was found that (1) a higher hip flexion-extension ratio was associated with lower energy cost and faster walking; (2) allowing the knee to flex significantly reduced the energy cost and increased the walking speed; (3) allowing the ankle to plantarflex during early stance phase reduced the knee flexing moment. The implications of these effects on the further development of hybrid functional electrical stimulation orthotic systems are discussed.
An in situ calibration protocol for ground-to-foot force measuring platforms is described. The methodology allows verification of the function of the force plate and allows accurate calibration for three force and moment channels. The effect of cross-sensitivity on recorded data is discussed along with the need for improvements in methodology to quantify this property.
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It is recognised that, in paraplegic walking with reciprocating gait orthoses, inadequate hip flexion angles may contribute to the low walking speed and high energy cost. In this study a new orthotic hip joint was developed which had a 2:1 flexion extension coupling ratio. Experiments on paraplegic subjects were conducted to evaluate this orthotic hip joint. It was found that the new hip joint was associated with a reduced energy cost and increased step length. A simple application of FES assisted hip flexion further increased walking speed and step length and reduced energy cost and crutch force impulse.
A triaxial flexible electrogoniometer has been developed to measure the three-dimensional angular motion of the shoulder joint during simulated activities of daily living. The motion of the elbow, forearm and wrist were also recorded and angle-angle diagrams were mathematically analysed to provide quantitative parameters regarding the control and co-ordination of the joints of the normal and the arthritic upper limb. Two parameters (slope and movement area quotient) were derived and used in the interpretation of joint motion during different activities.
OBJECTIVE: This study describes changes over a 12-month period in prevalence and frequency of alcohol and other drug use and correlates of change at 12 months in a sample of gay/bisexual men entering gay-identified outpatient substance abuse treatment. METHOD: A sequential sample of gay/bisexual men (n = 455) were recruited for a study in which substance use, sexual risk and psychological factors were assessed every 3 months. Changes in substance use were evaluated in 321 men who used in the 90 days before entering treatment and who completed at least one follow-up interview, whether or not they continued in treatment. RESULTS: At baseline, 95% of the sample reported alcohol use in the prior 90 days; 64%, marijuana/hashish use; 46%, amphetamine use; 33%, inhalant nitrites use; and 31%, cocaine use. Most men were polydrug users: 10% reported using only one drug (including alcohol); 39% used > or = 4 drugs. A marked reduction occurred in prevalence of use over time; declines on the order of 50% occurred in the first 90 days; prevalence then stabilized in remaining assessments. Frequency of usage by those reporting use of any given class of drugs also declined. No consistent predictors of reduction or cessation of use across different drug categories were found at 1 year. CONCLUSIONS: Substance use declined considerably in this sample. Given the scope of substance abuse problems among gay/bisexual men, and linkages to the HIV epidemic, considerable resources need to be focused on treatment and prevention for gay/bisexual men.
It is becoming increasingly common that fracture healing is modelled in the laboratory with an osteotomy in the diaphysis of the ovine tibia. External fixation is often used to hold the bones in these models, presenting the problem that the loads on such devices are poorly understood. To help investigate this, a unilateral device has been developed which is capable of measuring the two components of load considered to be the most important, that of axial compression and bending in the plane of the fixator. The device was found to be a rigid system and easy to apply, with the in-vivo measurements being straightforward. The estimated limits of error of the compression transducer are +37.9 N and -21.4 N and those of the bending transducer are +3.6 Nm and -4.2 Nm. Preliminary measurements showed the maximum load during normal walking to 345 N compression and 28 Nm in-plane bending.
This paper examines sexual risk-taking within a sample of sexually active gay and bisexual men entering substance abuse treatment (n = 383), and identifies correlates of unprotected anal sex within this group. Sexual risk-taking was high, with 55% of these men engaging in anal intercourse without a condom within a 90-day period. Correlates of unprotected anal sex varied somewhat when looking at unprotected anal sex with a primary partner only and with non-primary partners; substance use variables (number of drugs used, use of inhalant nitrites or stimulant drugs with sex, length of time since use of alcohol/drugs, loss of control problems associated with alcohol/drug use) appear to play more of a role in unprotected anal sex with non-primary partners. Overall, logistic regression analyses indicated that sexual risk was greater for those who were more sexually active, enjoyed unprotected anal sex with withdrawal prior to ejaculation, did not approve of sex outside of a love relationship, and identified themselves as more risky. In addition, those who reported more social problems due to substance use had fewer expectations that substance use increased risk, had been HIV-tested, and used reappraisal/problem-solving coping strategies showed greater risk with a primary partner only. Sexual risk with non-primary partners was greater for those who used more drugs, reported more difficulty avoiding high-risk sex when aroused and were HIV+. The paper discusses the implications of these findings for the design of sexual risk-reduction interventions.