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Biomedical subjects

R M Aspden

Publications and source records attributed to R M Aspden.

At least 55 records · Page 3Linked to original sources
PubMed1996

A comparison of methods for measuring trunk list. A simple plumbline is the best.

STUDY DESIGN: Trunk list was measured using three different techniques to compare accuracy, precision, and ease of use. OBJECTIVE: To obtain a reproducible technique for further studies of the nature, cause, and clinical relevance of trunk list. SUMMARY OF BACKGROUND DATA: Gravity-induced trunk list is a clinical sign that is frequently observed in patients with low back pain and has been associated with intervertebral disc lesions. METHODS: Patients with trunk list participated in a comparison of three techniques to determine list magnitude and direction. Paired measurements of trunk list were obtained from each patient using three techniques: a plumbline, a projected shadow, and the 3SPACE Isotrak (McDonnell Douglas Electronics Company, Colchester, VT). In addition, intra- and interobserver reliability of list measurement was assessed by comparison of paired measurements by each of two observers. RESULTS: List measurements assessed by the plumbline and the projected shadow techniques were not significantly different, but the Isotrak produced data that differed significantly (P < 0.05) from both of these techniques. Comparison of intra- and interobserver repeatability of list measurement using the plumbline technique indicated no significant difference between repeated measures by each observer or between two observers. CONCLUSIONS: A plumbline is the most useful instrument for measuring static trunk list, but its limitations and the need for standardization of measurement technique must be recognized.

Adult↗
PubMed1995

Matrix damage and chondrocyte viability following a single impact load on articular cartilage.

An impact load was applied to full-depth circular samples of articular cartilage in vitro and the effects of impact energy and velocity on matrix integrity and chondrocyte viability were studied. Following a severe impact, calculated to correspond to the energy density over the cartilage surface that might be expected in a man jumping off a 1-m-high wall, the tissue was grossly disrupted. It became elliptical, fissured, and flattened. Cartilage samples remaining attached to the underlying bone showed less damage at similar drop masses and heights. Chondrocyte viability was found to decrease linearly with increasing impact energy. Cartilage biopsies maintained in culture for up to 15 days following impact gained mass over the first 3 days which they did not subsequently lose. The gain in mass increased with the severity of impact and was due to an increased hydration of the tissue. Scanning electron microscopy and light microscopy showed fissures penetrating the tissue but which were never found to pass through the full depth. They were commonly oriented at about 45 degrees to the plane of the surface and gave the appearance of being deflected parallel to the surface on reaching the transition zone. This produced a "delaminating" effect where the surface zone was separating from the deep zone.

Animals↗
PubMed1995

Stiffening effects of cortical bone on vertebral cancellous bone in situ.

STUDY DESIGN: This study tested a theory about vertebral cancellous bone stiffness by performing experimental tests and comparing the results with the theoretical predictions. OBJECTIVES: To test experimentally a theoretical prediction that vertebral cancellous bone appears stiffer than would be expected from isolated tests because of the constraining effects of the cortical bone, to measure the magnitude of this strengthening effect and its dependency on tissue composition and density. SUMMARY OF BACKGROUND DATA: Vertebral bodies are composed mainly of cancellous bone surrounded by a thin shell of much stronger cortical bone. Little is known of the ways in which these two materials function synergistically to produce strong but light structures and why sometimes extensive damage to the cancellous bone has apparently little outward effect on vertebral body strength. METHODS: Cancellous bone from 45 lumbar vertebrae from a homogeneous group of pigs was tested in compression both in situ in the vertebral body and as an excised cylinder. The density and composition of the bone were then measured and correlation tested with both of the stiffness measurements. RESULTS: The cancellous bone in situ appears much stiffer than when isolated by a factor of about 4 (range, 1.6-12). No correlation was found between stiffness, either in situ or in isolation, and density, although density is predicted entirely by the volume fractions of water, organic, and mineral phases. CONCLUSIONS: Combining low density cancellous bone with stiffer, more dense cortical bone leads to a lightweight structure that is much stronger than might be expected from the isolated properties of its components.

Animals↗
PubMed1995

Trefoil configuration and developmental stenosis of the lumbar vertebral canal.

The midsagittal and interpedicular diameters and the trefoil shape of lumbar vertebrae of known age at death were measured in skeletons from a population aged between 1 and 70 years. All the trefoil configurations were at L5 with the exception of one at L4. The overall prevalence was 25%, but this shape was not generally apparent until adulthood. The midsagittal diameter in the trefoil canals was found to be significantly smaller than that in the unaffected canals. This did not change significantly after six years of age indicating that the cause of the trefoil configuration is probably present early in life. The trefoil shape was no more common in the spines of the elderly subjects. Our findings indicate that the trefoil configuration of the lumbar vertebral canal has a developmental origin and is not a consequence of degenerative processes.

Adult↗
PubMed1994

The growth of the lumbar vertebral canal.

STUDY DESIGN: This study examines the growth and development of the lumbar spinal canal with emphasis on early life. OBJECTIVE: Changes in dimensions of the canal were investigated throughout life. SUMMARY OF BACKGROUND DATA: Seven hundred and fifteen lumbar vertebrae were examined from the Spitalfield Collection of Skeletons at the Natural History Museum, London. METHODS: Unmagnified silhouette pictures were taken of the canals with a specially designed photographic box. Computerized image analysis provided the accurate measurements. RESULTS: Regarding the midsagittal diameter and the cross-sectional area, the cranial four lumbar vertebrae were already fully matured in infants. At L5 there was significant increase up to 4 years of age when the midsagittal diameter was even larger than in the adult. The interpedicular diameter significantly increased at L1 until 10 years of age, at the other levels until adulthood, as did the perimeter at L4 and L5 until 14 years of age. The shape of the canal was assessed by measuring the circularity, the 'trefoilness' and the situation of the centroid. The first measurement significantly decreased with age, the trefoilness increased until adulthood, and the centroid of the canal approached the vertebral body. In spines with spina bifida occulta, the lumbar canal was significantly larger proximal to the lesion than in the unaffected spines. CONCLUSION: The lumbar spinal canal exhausts its growth potential by infancy as regards the midsagittal diameter and the cross-sectional area. Thus, in the case of delayed development, it is not capable of catch-up growth.

Adolescent↗
PubMed1994

Fibre reinforcing by collagen in cartilage and soft connective tissues.

Mechanical support in animals is performed by connective tissues. The soft tissues consist of collagen fibres embedded in a highly hydrated proteoglycan gel. By considering them as fibrous composite materials, a unifying theme can be found to explain their mechanical behaviour in terms of their structure and composition. Interactions between fibres and matrix are essential to their functioning in this way. Calculations are made of the maximum stress transfer per D-period required to enable collagen fibres of a given axial ratio to provide effective reinforcing. Weak non-specific interactions are shown to be sufficient. A mechanical function is proposed for type X collagen in the epiphyseal growth plate on the basis that it modifies and supplements the properties of the type II fibrils. This provides extra reinforcing and, hence, a greater stiffness to the cartilage to compensate for the reduced amount of extracellular matrix.

Animals↗
PubMed1994

Collagen organization in the crural interosseous membrane and its relationship to fibular osteotomy.

The organization of collagen fibres in the crural interosseous membrane was measured using X-ray diffraction. The fibres were found to be highly aligned and steeply angled in a distal direction from tibia to fibula with a mean angle of 13 degrees. This organization will lead to a very stiff, ligament-like structure which will transmit forces to the tibia generated by the muscles attached to the fibula. It also suggests an optimum site for a fibular osteotomy about 4 cm distal to the tibial fracture site.

Aged↗
PubMed1994

Nerve traction during correction of knee flexion deformity. A case report and calculation.

We report the case of a child with cerebral palsy and spastic diplegia treated for bilateral fixed flexion of the knee by bilateral hamstring lengthening. An attempt to straighten the legs from 90 degrees to 20 degrees flexion damaged the sciatic nerve. There are no objective means of estimating how much deformity can be reduced safely. We present a method of calculating the extra strain in the sciatic nerve produced by reducing a flexion deformity. The result, combined with clinical judgement, provides guidelines for safe corrective surgery.

Cerebral Palsy↗
PubMed1993

Breast compression: a preliminary study.

X-Ray mammography is the technique employed to image breast tumours; it is the gold standard for both diagnosis and screening. To increase the sensitivity of the test and to reduce the dose of X-radiation, breast compression is used. The effect of squeezing a simple model of a breast in which there is an idealized spherical tumour volume is investigated; the cases where the lesion has both a smaller, and a larger compressibility than the surrounding tissues are considered. Surface strain is computed as a function of the deformation of the lesion from its spherical shape. Evidence from earlier studies is adduced to show that when the lesion is malignant care should be exercised to avoid the possibility of disseminating cancer cells by the application of compressive forces.

Breast Neoplasms↗
PubMed1993

Measurement of vertebral foraminal dimensions using three-dimensional computerized tomography.

The dimensions of lumbar intervertebral foramina were measured in cadaveric spines using three-dimensional computerized tomography. Six different image reconstruction protocols were used. The results were compared with measurements of the same foramina using calipers after dissection. All the three-dimensional computerized tomographic measurements underestimated the true foraminal dimensions. The best agreement, as well as the best images, were obtained using 4/3 slices and a reconstruction threshold of 300 Hounsfield Units. This method is not recommended for measurement of foraminal dimensions. However, there may be a use in assessment and planning surgical management.

Aged↗
PubMed1992

Study of tissue compression in breast phantoms: possible implications for the use of X-ray mammography as a method of imaging breast carcinoma.

A method is described of constructing a simple phantom breast containing an idealised tumour with elastic properties. The transparent tissues are compressed and evidence is adduced to show that with tissue compression the tumour boundary is subjected to a degree of strain the magnitude of which is dependent on the degree of deformation. Excessive compression can lead to fracture of the tumour. A literature survey reveals that malignant tissues are more delicate than normal tissues. The study underlines the need for care when using X-ray mammography with compression to image a cancer bearing breast, in order to avoid disseminating cancer cells via the circulation.

Breast Neoplasms↗
PubMed1991

Computer-controlled mechanical testing machine for small samples of biological viscoelastic materials.

Time dependency in the mechanical properties of viscoelastic materials means that a variety of tests is often required to fully characterize their properties. Computer control is the best way of controlling loads and displacements and the rate at which they are applied, as well as recording and analysing the data produced. This paper describes apparatus for measuring the viscoelastic properties of articular cartilage in compression which is readily adaptable to any small sample in which accurate strain measurements require small, carefully controlled displacements. An IBM-type microcomputer is used to control a stepper motor driving a ball screw with a positional accuracy of about 1 micron.

Biomechanical Phenomena↗
PubMed1991

Effects of mechanical load on cartilage matrix biosynthesis in vitro.

Cultured bovine articular cartilage full thickness explants were mechanically loaded, both statically and cyclically, at high frequency (2s of load with 2s intervals of no load) and low frequency (60s of load with 60s intervals of no load), at 1 MPa. Metabolic effects of the load were studied by radiolabeling and compared with non-loaded cartilage explants. High frequency load had a stimulatory effect on protein and proteoglycan synthesis while low frequency and static load showed decreased synthesis. Removing the load from the cultures restored synthesis to non-loaded control culture levels. No major differences in protein biosynthetic pattern were revealed, as determined by SDS-PAGE and fluorography, showing the generalized nature of the response.

Animals↗
PubMed1990

Comparison of structure, mechanical properties, and functions of lumbar spinal ligaments.

The organization of collagen in the supraspinous, interspinous, and longitudinal ligaments, as well as the ligamenta flava, in lumbar spines from human cadavers has been investigated by polarized light microscopy, scanning electron microscopy, and x-ray diffraction. These experiments were performed on ligaments in situ, with their bony attachments undisturbed, and on excised ligaments at a range of applied strains. Results were related to the composition (investigated by standard histologic techniques) and gross structures (investigated by light microscopy) of the ligaments. More importantly, the results were related to the mechanical properties of the ligaments, which include stiffness, failure conditions, stress relaxation, and hysteresis. Where necessary, results were supplemented by or compared with those obtained from pig ligaments. Mechanical properties were related to postural changes by ligament strains induced in cadaveric specimens, using results from the literature. Thus, ligament structures could be related to their physiologic functions.

Biomechanical Phenomena↗
PubMed1989

Structure and mechanical properties of the longitudinal ligaments and ligamentum flavum of the spine.

Stress-strain curves were recorded from anterior and posterior longitudinal ligaments and ligamenta flava dissected from pig lumbar spines. Ligaments were examined during extension by light microscopy, to observe crimp structure, and by X-ray diffraction, to determine collagen fibril orientations. Scanning electron microscopy (SEM) was used to examine ligaments fixed at high and low strains. Initial stages of ligament extension involved alignment of collagen fibrils. Collagen fibrils in unstrained ligamentum flavum were much more disoriented than in the longitudinal ligaments. Thus, fibril alignment, and consequent stiffening, occurred at much higher strains than for longitudinal ligaments, allowing ligamentum flavum to exploit the extensibility of its elastin.

Animals↗