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Biomedical subjects

R B Ashman

Publications and source records attributed to R B Ashman.

At least 55 records · Page 3Linked to original sources
PubMed1994

Biomechanical properties of small bone screws.

PURPOSE: To evaluate systematically the biomechanical properties of 13 popular screw designs, ranging from 0.8 to 2.0 mm in diameter. METHODS: Screws were characterized in terms of external, core, and drill diameter; cutting flute and head design; material; pitch, thread depth; and height of shank (unthreaded portion) and shank with plate. They were tested in standardized bone specimens (2 x 2.5cm slabs of fresh bovine femur) 1, 2, 3, and 4-mm thick. For each screw-bone thickness combination, 10 trials were conducted to determine push-out force (POF) and another 10 trials to determine insertion (IT) and maximum torque (MT) yielding a total of 1,040 tests. RESULTS: Among the 13 different screws, in 1-mm thick bone, both the lowest (108.5 N) and highest (294.9 N) POF were created by 2-mm screws (P < .001); that with the lowest POF had a long unthreaded shank and pitch, that with highest POF had a short unthreaded shank and pitch. Screws with 0.8- to 1.5-mm diameters showed no differences in POF. The 2-mm screw with the lowest POF also had the lowest MT in 1-mm thick bone compared with the other 2-mm screws (P < .001). In thicker bones (> 2 mm), two 2-mm screws showed 30% to 50% lower MT than the other same size screws (P < .001) because their head slots stripped easily. When all screws were considered together for a particular bone thickness, torque was strongly predicted by screw diameter (MT: r = .94, P < .001; IT: r = 0.92, P < .001). Screws with the same diameters varied significantly in IT because of differences in self-tapping cutting flute design. CONCLUSION: External diameter, unthreaded shank height, head slot, and self-tapping cutting flute design had the greatest impact on screw strength and efficiency in thin cortical bone. Thread depth, core diameter, and metal type did not affect performance significantly. Under these highly standardized in vitro conditions, the ideal 2-mm screw has an unthreaded shank that is as short as possible, and the pitch is about 0.8 mm. Additional aspects of a clinical situation beside holding strength must, however, be considered when choosing a screw.

Analysis of Variance↗
PubMed1994

Endothelial cell proliferation associated with lesions of murine systemic candidiasis.

Neovascularization is associated with tumor growth and some inflammatory diseases but has not been reported to be induced by infectious agents. In a mouse model of systemic Candida albicans infection, extensive endothelial cell proliferation was seen in the periphery of brain abscesses and in the areas of fungal pyelonephritis in the kidney. This finding is important for an understanding of the pathogenesis of fungal infections and may contribute to an analysis of the mechanisms of angiogenesis.

Animals↗
PubMed1994

In vitro comparison of the effect of parallel and divergent transfixation pins on breaking strength of equine third metacarpal bones.

Breaking strength (torque at failure) of equine third metacarpal bones, with transfixation pins placed parallel in the frontal plane and 30 degrees divergent from the frontal plane, was determined in vitro. Two transfixation pins were placed through the distal metaphysis, using a jig designed to drill the holes in the assigned configuration. Paired metacarpal bones II through IV from 12 horses were tested in torsion. The torsional moment of the force applied through the transfixation pins at failure was compared for each limb. Metacarpal bones with divergent pins were significantly (P = 0.030) stronger, compared with those with parallel pins. Metacarpal bones with parallel pins failed with longitudinal oblique fractures through a proximal bone-pin interface, whereas those with divergent pins failed with more comminuted fractures through multiple bone-pin interfaces.

Animals↗
PubMed1994

In vitro comparison of the standard short limb cast and three configurations of short limb transfixation casts in equine forelimbs.

Axial stability of equine oblique proximal phalangeal osteotomies with application of the standard short limb cast or 1 of 3 configurations of transfixation casts was determined in vitro. Transfixation cast methods included use of parallel pins, divergent pins, or parallel pins incorporating a metal walking bar. Displacement at the osteotomy was recorded for each limb at 4,448 N. Standard short limb casts provided significantly (P = 0.0002) less axial stability than did any form of transfixation cast. Significant differences were not found between the 3 transfixation casts.

Animals↗
PubMed1994

Interference fixation versus postfixation of bone-patellar tendon-bone grafts for anterior cruciate ligament reconstruction. A biomechanical comparative study in porcine knees.

This study compares biomechanical characteristics of interference screw fixation to "postfixation" (sutures tied over cancellous screw and washer) of bone-patellar tendon-bone grafts in porcine anatomic specimen knees. Maximum pull-out strength (ultimate failure load), displacement of the bone graft at 110 N of force, and mode of failure were compared in a progressive load to failure test. Interference screw fixation demonstrated statistically significantly (p = 0.04) higher mean ultimate failure loads (535 N) compared to postfixation (309.1 N). Interference fixation also demonstrated statistically significantly (p = 0.0003) less displacement of the bone graft at 110 N of force (0.32 mm vs. 2.21 mm). All failures occurred at the fixation site. The authors conclude that interference fixation is stronger than postfixation and, in the immediate postoperative period, should better protect the graft from loosening after anterior cruciate ligament reconstruction, improving stability and allowing more aggressive rehabilitation.

Animals↗
PubMed1993

A preliminary investigation of shape memory alloys in the surgical correction of scoliosis.

Nitinol, a shape memory alloy, is flexible at low temperatures but retains its original shape when heated. This offers interesting possibilities for scoliosis correction. Of the shape memory alloys, nitinol is the most promising medically because of biocompatibility and the ability to control transition temperature. In vivo: Six goats with experimental scoliosis were instrumented with 6-mm nitinol rods. The rods were transformed, and the scoliosis corrected, in the awakened goats by 450-kHz radio frequency induction heating. The curves averaged 41 degrees before instrumentation, 33 degrees after instrumentation, and 11 degrees after rod transformation. The animals tolerated the heating without discomfort, neurologic injury, or evidence of thermal injury to the tissues or the spinal cord. In vitro: Nitinol rods were tested under both constant deflection and constant loading conditions and plotted temperature versus either force or displacement. The 6-mm rod generated forces of 200 N. The 9-mm rod generated up to 500 N. We safely coupled shape memory alloy transformation to the spine and corrected an experimental spinal deformity in awake animals. The forces generated can be estimated by the rod's curvature and temperature. The use of shape memory alloys allows continuous neurologic monitoring during awake correction, true rotational correction by rod torsion, and the potential option of periodic correction to take advantage of spinal viscoelasticity and the potential of true rotational correction by rod torsion.

Alloys↗
PubMed1993

Elastic properties of human supraorbital and mandibular bone.

Elastic constants, including the elastic modulus, the shear modulus, and Poisson's ratio, were measured on human craniofacial bone specimens obtained from the supraorbital region and the buccal surfaces of the mandibles of unembalmed cadavers. Constants were determined using an ultrasonic wave technique in three directions relative to the surface of each sample: 1) normal, 2) tangential, and 3) longitudinal. Statistical analysis of these elastic constants indicated that significant differences in the relative proportions of elastic properties existed between the regions. Bone from the mandible along its longitudinal axis was stiffer than bone from the supraorbital region. Directional differences in both locations demonstrated that cranial bone was not elastically isotropic. It is suggested that differences in elastic properties correspond to regional differences in function.

Elasticity↗
PubMed1993

Young's modulus of trabecular and cortical bone material: ultrasonic and microtensile measurements.

An ultrasonic technique and microtensile testing were used to determine the Young's modulus of individual trabeculae and micro-specimens of cortical bone cut to similar size as individual trabeculae. The average trabecular Young's modulus measured ultrasonically and mechanically was 14.8 GPa (S.D. 1.4) and 10.4 (S.D. 3.5) and the average Young's modulus of microspecimens of cortical bone measured ultrasonically and mechanically was 20.7 GPa (S.D. 1.9) and 18.6 GPa (S.D. 3.5). With either testing technique the mean trabecular Young's modulus was found to be significantly less than that of cortical bone (p < 0.0001). However, the specimens were dried before microtensile testing so Young's modulus values may have been greater than those of trabeculae in vivo. Using Young's modulus measurements obtained from 450 cubes of cancellous bone and 256 cubes of cortical bone, Wolff's hypothesis that cortical bone is simply dense cancellous bone was tested. A multiple regression analysis that controlled for group membership showed that Young's modulus of cortical bone cannot be extrapolated from the Young's modulus vs density relationship for cancellous bone, yet the Young's modulus of trabeculae can be predicted by extrapolation from the relationship between Young's modulus vs density of the cancellous bone. These results suggest that when considered mechanically, cortical and trabecular bone are not the same material.

Aged↗
PubMed1993

Patterns of resistance to Candida albicans in inbred mouse strains.

Candida albicans infections were established in eight inbred strains of mice. Using established histological criteria, only two strains (AKR and CBA/CaH) were found to exhibit severe lesions. The remainder showed only mild tissue damage. Deaths occurred in three strains: CBA/CaH, A/J and DBA/2. The last two strains lack the important complement component C5. Colony counts in the brain varied widely between strains and showed no correlation with the extent or severity of tissue destruction. However, strains lacking C5 had a significantly greater fungal burden in the brain than C5-sufficient mice. The data are discussed in relation to concepts of susceptibility and resistance to C. albicans in experimental infections in mice.

Animals↗
PubMed1993

Strain differences in the severity of lesions in murine systemic candidiasis correlate with the production of functional gamma interferon by Candida-activated lymphocytes in vitro.

BALB/c mice exhibit mild, and CBA/CaH mice exhibit severe tissue lesions after systemic infection with the yeast Candida albicans. There is considerable evidence that recovery from primary infection is associated with the development of cell-mediated immune responses in the infected mice, and that cytokines produced by T lymphocytes augment the phagocytic and candidacidal functions of macrophages and polymorphonuclear leukocytes. To determine whether the severity of lesions in the two inbred strains was associated with differences in cytokine production, lymphocytes were obtained from the spleens of normal and immune mice, activated with Candida antigens in vitro, and functional cytokines identified by bioassay. mRNA obtained from the activated lymphocytes was also screened for cytokine-specific sequences by S1-nuclease protection analysis. mRNA for IL-3 and IFN-gamma, but not IL-2 or IL-4, was detected in lymphocytes from both BALB/c and CBA/CaH mice, but only lymphocytes from primary and secondary cultures of BALB/c cells showed Candida-specific induction of IFN-gamma bioactivity. These results suggest that, in this murine model of systemic candidiasis, the propensity to develop severe lesions exhibited by CBA/CaH mice may be a consequence of some form of posttranscriptional regulation of gamma-interferon production.

Animals↗
PubMed1993

Genetic, structural, and functional studies of a C3-like protein in the marsupial Setonix brachyurus.

A monospecific goat antiserum was prepared against a putative C3 protein (QuC3) from serum of the Western Australian macropod Setonix brachyurus (quokka) using the classical method previously used to produce antiserum against C3 from other mammalian species. Sodium dodecyl sulphate-polyacrylamide gel electrophoretic analysis of reduced immunoprecipitated QuC3 revealed two polypeptide chains with an estimated M(r) of 128,000 and 82,000, respectively--presumably reflecting subunit molecules similar to the C3 alpha and beta subunits found in other mammalian species. No variation in the size of either of the QuC3 alpha or beta subunits was found in different quokka serum samples. Furthermore, no variation in the electrophoretic mobility of QuC3 was detected amongst the same samples using a standard immunofixation electrophoretic technique. The addition of zymosan or immune complexes to fresh quokka serum resulted in activation of QuC3. Immune complex mediated activation of QuC3 was inhibited by the addition of EDTA and Mg(2+)-EGTA. By contrast, EDTA only inhibited activation of QuC3 following incubation of fresh quokka serum with zymosan, suggesting that the quokka has a classical and an alternative C3 activation pathway, similar to those found in eutherian mammals. This study has shown for the first time that one of the macropod marsupials (S. brachyurus) has a C3-like protein with similar structural and functional characteristics to C3 found in eutherian mammals. However, unlike C3 in other mammalian species, genetic variability of the structure of the quokka C3-like protein may be restricted.

Animals↗
PubMed1992

Adaptations of young adult rat cortical bone to 14 days of spaceflight.

To determine whether mature humeral cortical bone would be modified significantly by an acute exposure to weightlessness, adult rats (110 days old) were subjected to 14 days of microgravity on the COSMOS 2044 biosatellite. There were no significant changes in peak force, stiffness, energy to failure, and displacement at failure in the flight rats compared with ground-based controls. Concentrations and contents of hydroxyproline, calcium, and mature stable hydroxylysylpyridinoline and lysylpyridinoline collagen cross-links remained unchanged after spaceflight. Bone lengths, cortical and endosteal areas, and regional thicknesses showed no significant differences between flight animals and ground controls. Our findings suggest that responsiveness of cortical bone to microgravity is less pronounced in adult rats than in previous spaceflight experiments in which young growing animals were used. We hypothesize that 14 days of spaceflight may not be sufficient to impact the biochemical and biomechanical properties of cortical bone in the mature rat skeleton.

Adaptation, Physiological↗
PubMed1991

Measurement of mechanical properties of bone material in vitro by ultrasound reflection: methodology and comparison with ultrasound transmission.

An ultrasound reflection technique was designed and implemented to study the mechanical properties of bone material. The technique uses the fact that an ultrasound beam produced in water undergoes total internal reflection off a bone sample at a critical angle formally related to the velocity of a pressure wave in bone. When the plane of scattering is rotated around the normal to the sample surface, the critical angle varies with a periodic dependence dictated by the intrinsic symmetry of the bone structure at the point being examined. Most current measurements of sound velocity are made using transmission techniques. A double-blind intercomparison between this technique and a transmission technique, which was previously validated against tensile mechanical testing, was performed for samples of isotropic materials and of human cortical bone. Strong correlations were found for both sets of samples. For the isotropic materials the velocities were approximately equal, but for bone they were on average 11% higher in reflection than in transmission. This was the result both of the higher frequency employed in reflection (3.5 rather than 2.25 MHz) and of the different effects of sample imperfections on the two measurements. In particular, the reflection technique used in this work studied the surface of the sample, but the ultrasound beam in the transmission method propagated through its interior. In assessing the mechanical properties of bone specimens by ultrasound, the reflection technique samples a discrete bone surface element and the transmission method analyzes the entire volume of the specimen. Thus the reflection technique may yield a measure of the mechanical property of bone trabeculae that is largely unaffected by the mass of the entire specimen, but mass and the structural density of the specimen affect the transmission method.

Biomechanical Phenomena↗
PubMed1991

Enhancement of MHC class II antigen expression by exposure to Candida albicans.

In oral infections with the yeast Candida albicans, the expression of MHC class II antigens on keratinocytes has been reported to be enhanced. In the present experiments, exposure to C. albicans or its products in vitro was found to increase the expression of class II MHC antigens on thioglycollate-induced mouse macrophages, and on LK cells (an antigen-presenting cell line). The implications of this finding for the understanding of immunoregulation and susceptibility to C. albicans infection are discussed.

Animals↗
PubMed1991

Murine candidiasis: sex differences in the severity of tissue lesions are not associated with levels of serum C3 and C5.

Mice deficient in the fifth component of complement are known to be extremely susceptible to lethal challenge with Candida albicans. However, male mice, that have significantly higher concentrations of serum C5 than females, were markedly more susceptible to infection. This difference was observed in both susceptible (CBA/H) and resistant (BALB/c) mice. Levels of serum C3 likewise showed no correlation with susceptibility.

Animals↗