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S R Stock

Publications and source records attributed to S R Stock.

At least 19 recordsLinked to original sources
PubMed2006

Micromechanical response of mineral and collagen phases in bone.

We report the first simultaneous quantification of Young's modulus in the separate material phases of bone: collagen and carbonated hydroxyapatite. High-energy X-ray scattering and in situ loading revealed macroscopic, mineral, and collagen Young's moduli (90% confidence limit) for a canine fibula equaled 24.7(0.2) GPa, 38.2(0.5) GPa {for 00.4 and 43.6(1.4) GPa for 22.2}, and 18(1.2) GPa, respectively. The mineral contained compressive residual stresses on the order of -60 to -80 MPa before loading and had a stress enhancement (ratio of internal to applied stress) between 2.0 and 2.3. The diffraction peak width increased with increasing applied stress, mainly along the bone's longitudinal direction, and peak widths returned to pre-deformation values when load was removed. In a second fibula section from the same animal, the mineral's internal stress changed from -50 MPa (22.2 reflection) to -75 MPa (00.4) just after removal from formalin to -10 MPa after eight hours immersion in phosphate-buffered saline; the corresponding change in collagen D-spacing DeltaD/D equaled 4.2x10(-3).

Animals↗
PubMed2006

Mapping of magnesium and of different protein fragments in sea urchin teeth via secondary ion mass spectroscopy.

Mature portions of sea urchin are comprised of a complex array of reinforcing elements yet are single crystals of high and very high Mg calcite. How a relatively poor structural material (calcite) can produce mechanically competent structures is of great interest. In teeth of the sea urchin Lytechinus variegatus, we recorded high-resolution secondary ion mass spectrometry (SIMS) maps of Mg, Ca ,and specific amino acid fragments of mineral-related proteins including aspartic acid (Asp). SIMS revealed strong colocalization of Asp residues with very high Mg. Demineralized specimens showed serine localization on membranes between crystal elements and reduced Mg and aspartic acid signals, further emphasizing colocalization of very high Mg with ready soluble Asp-rich protein(s). The association of Asp with nonequilibrium, very high magnesium calcite provides insight to the makeup of the macromolecules involved in the growth of two different composition calcites and the fundamental process of biomineralization.

Animals↗
PubMed2005

Transmission electron microscopy characterization of macromolecular domain cavities and microstructure of single-crystal calcite tooth plates of the sea urchin Lytechinus variegatus.

The calcite plates and prisms in Lytechinus variegatus teeth form a complex biocomposite and employ a myriad of strengthening and toughening strategies. These crystal elements have macromolecule-containing internal cavities that may act to prevent cleavage. Transmission electron microscopy employing a small objective aperture was used to quantify several characteristics of these cavities. Cavity diameters ranged from 10 to 225 nm, the mean cavity diameter was between 50 and 60 nm, and cavities comprised approximately 20% of the volume of the crystal. Some cavities exhibited faceting and trace analysis identified these planes as being predominately of {1014} type. Through focus series of micrographs show the cavities were homogeneously distributed throughout the foil. The electron beam decomposed a substance within cavities and this suggests that these cavities are filled with a hydrated organic phase.

Animals↗
PubMed2005

Internal strains and stresses measured in cortical bone via high-energy X-ray diffraction.

High-energy synchrotron X-ray diffraction was used to study internal stresses in bone under in situ compressive loading. A transverse cross-section of a 12-14 year old beagle fibula was studied with 80.7 keV radiation, and the transmission geometry was used to quantify internal strains and corresponding stresses in the mineral phase, carbonated hydroxyapatite. The diffraction patterns agreed with tabulated patterns, and the distribution of diffracted intensity around 00.2/00.4 and 22.2 diffraction rings was consistent with the imperfect 00.1 fiber texture expected along the axis of a long bone. Residual compressive stress along the bone's longitudinal axis was observed in the specimen prior to testing: for 22.2 this stress equaled -95 MPa and for 00.2/00.4 was between -160 and -240 MPa. Diffraction patterns were collected for applied compressive stresses up to -110 MPa, and, up to about -100 MPa, internal stresses rose proportionally with applied stress but at a higher rate, corresponding to stress concentration in the mineral of 2.8 times the stress applied. The widths of the 00.2 and 00.4 diffraction peaks indicated that crystallite size perpendicular to the 00.1 planes increased from t=41 nm before stress was applied to t=44 nm at -118 MPa applied stress and that rms strain epsilon(rms) rose from 2200 muepsilon before loading to 4600 muepsilon at the maximum applied stress. Small angle X-ray scattering of the unloaded sample, recorded after deformation was complete, showed a collagen D-period of 66.4 nm (along the bone axis).

Animals↗
PubMed2005

Atorvastatin inhibits calcification and enhances nitric oxide synthase production in the hypercholesterolaemic aortic valve.

OBJECTIVE: To study in a rabbit model the expression of endothelial nitric oxide synthase (eNOS) in association with the development of calcification of the aortic valve, and to assess the effects of atorvastatin on eNOS expression, nitrite concentration, and aortic valve calcification. METHODS: Rabbits (n = 48) were treated for three months: 16, forming a control group, were fed a normal diet; 16 were fed a 0.5% (wt/wt) high cholesterol diet; and 16 were fed a 0.5% (wt/wt) cholesterol diet plus atorvastatin (2.5 mg/kg/day). The aortic valves were examined with eNOS immunostains and western blotting. Cholesterol and high sensitivity C reactive protein (hsCRP) concentrations were determined by standard assays. Serum nitrite concentrations were measured with a nitric oxide analyser. eNOS was localised by electron microscopy and immunogold labelling. Calcification in the aortic valve was evaluated by micro-computed tomography (CT). RESULTS: Cholesterol, hsCRP, and aortic valve calcification were increased in the cholesterol fed compared with control animals. Atorvastatin inhibited calcification in the aortic valve as assessed by micro-CT. eNOS protein concentrations were unchanged in the control and cholesterol groups but increased in the atorvastatin treated group. Serum nitrite concentrations were decreased in the hypercholesterolaemic animals and increased in the group treated with atorvastatin. CONCLUSION: These data provide evidence that chronic experimental hypercholesterolaemia produces bone mineralisation in the aortic valve, which is inhibited by atorvastatin.

Animals↗
PubMed2004

MicroCT quantification of in vitro bone resorption of neonatal murine calvaria exposed to IL-1 or PTH.

This study investigated how effectively a laboratory microCT (X-ray micro-computed tomography) system can quantify bone resorption in an in vitro calvarial model and how well this measure correlates with a conventional assay for calcium release (fluorometric titration). In vitro bone resorption in neonatal murine calvaria was quantified for 0.3 or 1.0 nM interleukin-1 (IL-1) or for 1.0 or 10.0 nM parathyroid hormone (PTH) treatment. Compared to control calvaria, a significantly greater fraction F of the calvarial "shell" (computed from the volumetric microCT data) was resorbed in treated calvaria of 5- to 7-day-old pups from the same litter. Excellent correlation (R2 = 0.8234) was observed between F and calcium release, and, unlike the calcium assay, the 3-D maps revealed where bone was resorbed. Mineral was preferentially lost near the sutures, and areas away from the suture were left relatively intact. MicroCT of calvaria before and after 96 h culture demonstrated that this X-irradiation neither increased control resorption nor prevented responses in the treated calvaria. Observations on calvaria from intact mice aged 1, 3, 5, 8, and 11 days showed uniformly distributed mineral (not a pronounced patchwork of "high" and "low" mineral regions) and increasing levels of mineral with age; this suggested that the spatial patterns of resorption were not related to inhomogeneities in the starting mineral distribution.

Animals↗
PubMed2003

Multiple microscopy modalities applied to a sea urchin tooth fragment.

Two synchrotron X-ray microscopy methods, phase-contrast microradiography (the propagation method) and absorption microCT (high-resolution computed tomography or microtomography), and laser-scanning confocal microscopy (visible wavelength) were used to study a fragment of the keel of a tooth of the sea urchin Lytechinus variegatus. Stripes observed in the phase-contrast images of the fragment were also seen in confocal micrographs. MicroCT showed that the stripes were due to two parallel planar arrays of low-absorption channels within the bulk of the keel. In the phase microradiographs, maximum contrast stripes appear when a channel image from one row coincides with a channel image from the second row; otherwise, contrast is minimal. Long channels do not appear to have been observed previously in keels of sea urchin teeth.

Animals↗
PubMed2003

Synchrotron X-ray studies of the keel of the short-spined sea urchin Lytechinus variegatus: absorption microtomography (microCT) and small beam diffraction mapping.

In sea urchin teeth, the keel plays an important structural role, and this paper reports results of microstructural characterization of the keel of Lytechinus variegatus using two noninvasive synchrotron x-ray techniques: x-ray absorption microtomography (microCT) and x-ray diffraction mapping. MicroCT with 14 keV x-rays mapped the spatial distribution of mineral at the 1.3 microm level in a millimeter-sized fragment of a mature portion of the keel. Two rows of low absorption channels (i.e., primary channels) slightly less than 10 microm in diameter were found running linearly from the flange to the base of the keel and parallel to its sides. The primary channels paralleled the oral edge of the keel, and the microCT slices revealed a planar secondary channel leading from each primary channel to the side of the keel. The primary and secondary channels were more or less coplanar and may correspond to the soft tissue between plates of the carinar process. Transmission x-ray diffraction with 80.8 keV x-rays and a 0.1 mm beam mapped the distribution of calcite crystal orientations and the composition Ca(1-x)Mg(x)CO(3) of the calcite. Unlike the variable Mg concentration and highly curved prisms found in the keel of Paracentrotus lividus, a constant Mg content (x = 0.13) and relatively little prism curvature was found in the keel of Lytechinus variegatus.

Animals↗
PubMed2003

Three-dimensional microarchitecture of the plates (primary, secondary, and carinar process) in the developing tooth of Lytechinus variegatus revealed by synchrotron X-ray absorption microtomography (microCT).

This paper reports the first noninvasive, volumetric study of entire cross-sections of a sea urchin tooth in which the individual calcite structural elements could be resolved. Two cross-sectionally intact fragments of a Lytechinus variegatus tooth were studied with synchrotron microCT (microcomputed tomography) with 1.66 microm voxels (volume elements). These fragments were from the plumula, that is the tooth zone with rapidly increasing levels of mineral; one fragment was from a position aboral of where the keel developed and the second was from the zone where the keel was developing. The primary plates, secondary plates, carinar process plates, prisms, and elements of the lamellar-needle complex were resolved. Comparison of the microCT data with optical micrographs of stained thin sections confirmed the identifications and measured dimensions of the characteristic microarchitectural features. The interplay of reinforcing structures (plates and prisms) was more clearly revealed in the volumetric numerical data sets than in single or sequential slices. While it is well known that the primary plates and prisms in camarodont teeth are situated to improve resistance to bending (which can be termed primary bending), the data presented provide a new understanding of the mechanical role of the carinar process plates, that is, a geometry consistent with that required in the keel to resist lateral or transverse bending of the tooth about a second axis. The increase in robustness of teeth incorporating lateral keel reinforcement suggests that the relative development of carinar processes (toward a geometry similar to that of L. variegatus) is a character which can be used to infer which sea urchins among the stirodonts are most primitive and among the camarodonts which are more primitive.

Animals↗
PubMed2003

X-ray microCT study of pyramids of the sea urchin Lytechinus variegatus.

This paper reports results of a novel approach, X-ray microCT, for quantifying stereom structures applied to ossicles of the sea urchin Lytechinus variegatus. MicroCT, a high resolution variant of medical CT (computed tomography), allows noninvasive mapping of microstructure in 3-D with spatial resolution approaching that of optical microscopy. An intact pyramid (two demipyramids, tooth epiphyses, and one tooth) was reconstructed with 17 microm isotropic voxels (volume elements); two individual demipyramids and a pair of epiphyses were studied with 9-13 microm isotropic voxels. The cross-sectional maps of a linear attenuation coefficient produced by the reconstruction algorithm showed that the structure of the ossicles was quite heterogeneous on the scale of tens to hundreds of micrometers. Variations in magnesium content and in minor elemental constitutents could not account for the observed heterogeneities. Spatial resolution was insufficient to resolve the individual elements of the stereom, but the observed values of the linear attenuation coefficient (for the 26 keV effective X-ray energy, a maximum of 7.4 cm(-1) and a minimum of approximately 2 cm(-1) away from obvious voids) could be interpreted in terms of fractions of voxels occupied by mineral (high magnesium calcite). The average volume fraction of mineral determined for a transverse slice of the demipyramid near where it joins an epiphysis was 0.46; for a slice 3.3 mm adoral it was 0.70. Local volume fractions of mineral approached 1, and, away from resolvable voids, considerable portions of the demipyramids had volume fractions of calcite at or below approximately 0.33. MicroCT imaging of a demipyramid before and after infiltration with a high absorptivity fluid (sodium polytungstate) confirmed the determination of the volume fractions of minerals.

Animals↗
PubMed2002

X-ray absorption microtomography (microCT) and small beam diffraction mapping of sea urchin teeth.

Two noninvasive X-ray techniques, laboratory X-ray absorption microtomography (microCT) and X-ray diffraction mapping, were used to study teeth of the sea urchin Lytechinus variegatus. MicroCT revealed low attenuation regions at near the tooth's stone part and along the carinar process-central prism boundary; this latter observation appears to be novel. The expected variation of Mg fraction x in the mineral phase (calcite, Ca(1-x)Mg(x)CO(3)) cannot account for all of the linear attenuation coefficient decrease in the two zones: this suggested that soft tissue is localized there. Transmission diffraction mapping (synchrotron X-radiation, 80.8 keV, 0.1 x 0.1mm(2) beam area, 0.1mm translation grid, image plate area detector) simultaneously probed variations in 3-D and showed that the crystal elements of the "T"-shaped tooth were very highly aligned. Diffraction patterns from the keel (adaxial web) and from the abaxial flange (containing primary plates and the stone part) differed markedly. The flange contained two populations of identically oriented crystal elements with lattice parameters corresponding to x=0.13 and x=0.32. The keel produced one set of diffraction spots corresponding to the lower x. The compositions were more or less equivalent to those determined by others for camarodont teeth, and the high Mg phase is expected to be disks of secondary mineral epitaxially related to the underlying primary mineral element. Lattice parameter gradients were not noted in the keel or flange. Taken together, the microCT and diffraction results indicated that there was a band of relatively high protein content, of up to approximately 0.25 volume fraction, in the central part of the flange and paralleling its adaxial and abaxial faces. X-ray microCT and microdiffraction data used in conjunction with protein distribution data will be crucial for understanding the properties of various biocomposites and their mechanical functions.

Animals↗
PubMed2000

Classification criteria and severity assessment in work-associated upper extremity disorders: methods matter.

Work-associated musculoskeletal disorders of the upper extremity are common and disabling. Research on these disorders is needed and requires valid methods of classification of the disorders for epidemiologic studies and measurement of their impact on functional status. This commentary discusses the methodologic aspects of classification and functional status assessment in upper extremity musculoskeletal disorders.

Classification↗
PubMed1999

The association between cigarette smoking and back pain in adults.

STUDY DESIGN: A retrospective cohort study of adolescent idiopathic scoliosis. A comparison group of persons without scoliosis was also selected randomly from the general population. OBJECTIVES: To estimate the association between level of cigarette smoking and the prevalence and severity of back pain. METHODS: A postal questionnaire was used to elicit information on smoking histories, a variety of indices of low back pain, and potential confounding factors. The association between smoking and back pain was estimated separately for men and women in the cohort and in the comparison group using ordinal regression models. RESULTS: The questionnaire was completed by 1287 women and 184 men who had adolescent idiopathic scoliosis and by 1130 women and 621 men in the comparison population who did not have scoliosis. Statistically significant associations between back pain and current cigarette smoking were found in the two groups of women and men with scoliosis, but not among men selected from the general population. In the three former groups, proportional odds ratios comparing current smokers to persons who never smoked ranged from 1.4 to 1.9. Among current smokers, the prevalence of back pain increased with cigarette consumption, and the proportional odds ratios ranged from 1.2 to 1.8 per 10 pack-years (no. of cigarettes smoked per day x no. of years/20). In these three groups, intensity, frequency, and duration of episodes of back pain also were found to increase with smoking consumption. CONCLUSION: The finding that smokers have more frequent episodes of back pain may imply that smoking exacerbates back pain, and the observation that stronger associations between back pain and smoking were found in the scoliosis cohort suggests that smoking may have a greater impact on persons with damaged spines.

Adolescent↗
PubMed1996

Can Dupuytren's contracture be work-related?: review of the evidence.

Dupuytren's contracture (DC) is a disease of the palmar fascia resulting in thickening and contracture of fibrous bands on the palmar surface of the hands and fingers. For decades, a controversy has existed regarding whether acute traumatic injury or cumulative biomechanical work exposure can contribute to the development of this disorder. To address this controversy, this review considers the following questions: Is there evidence that DC is associated with 1) frequent or repetitive manual work; and 2) hand vibration? The published literature was searched for studies meeting the following criteria: 1) in English or having an English abstract; 2) controlled studies; 3) DC an identified health outcome studied; and 4) the study group exposed to repetitive or frequent manual work, vibration, or acute traumatic injury. Relevant non-English articles identified through English abstracts were translated. The validity of studies meeting the selection criteria was assessed using a series of questions adapted from those of Stock [1991: Am J Ind Med 19:87-107]. Studies that met a priori minimum levels of methodologic quality were taken into account to reach conclusions with respect to the above questions. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for each study. Ten studies met the initial selection criteria. Of these, four studies met the criteria for methodologic quality, one addressing the relationship between manual work and DC, and three studies of vibration and DC. No controlled studies of acute trauma and DC were identified. Bennett [1982: Br J Ind Med 39:98-100] found the prevalence of DC at a British PVC bagging and packing plant in which workers were exposed to repetitive manual work to be 5.5 times that at a local plant without packing, and twice the expected prevalence in a U.K. working population previously studied by Early [1962: J Bone Joint Surg 44B:602-613]. DC was observed more frequently among vibration white finger claimants than controls by Thomas and Clarke [1992: J Soc Occup Med 42:155-158] (OR, 2.1; 95% CI, 1.1-3-9), and more frequently among vibration-exposed workers than controls by Bovenzi et al. [1994: Occup Environ Med 51:603-611] (OR, 2.6 95% CI, 1.2-5.5). Cocco et al [1987: Med Lav 78:386-392] found that a history of vibration exposure occurred more frequently among cases of DC than among controls (OR, 2.3; 95% CI, 1.5-4.4). The latter two studies presented some evidence of a dose-response relationship. There is good support for an association between vibration exposure and DC.

Causality↗
PubMed1996

Review of applicability of existing functional status measures to the study of workers with musculoskeletal disorders of the neck and upper limb.

Both epidemiologic studies of the factors that contribute to the development of work-related musculoskeletal disorders of the neck and upper limb and intervention studies that test the effectiveness of workplace ergonomic and organizational changes are needed to provide empiric evidence for preventive strategies. This study reviews the relevance and comprehensiveness of existing functional status instruments for epidemiologic studies of work-related neck and upper limb disorders. Twelve domains were identified as the major areas of life affected by workers' neck and upper extremity disorder(s): work, household and family responsibilities, self-care, transportation/driving, sexual activity, sleep, social activities, recreational activities, mood, self-esteem, financial effects, and iatrogenic effects of assessments and treatment. Fifty-two functional status instruments were identified. Of these, 21 met the specified criteria as potentially relevant and were rated on the 3-point scale for relevance and comprehensiveness for each domain. None of the instruments covered all 12 domains adequately.

Arm Injuries↗
PubMed1993

Occupational dust exposure and chronic obstructive pulmonary disease. A systematic overview of the evidence.

The object of this study was to assess the relationship between occupational dust exposure and chronic obstructive pulmonary disease (COPD). Studies were identified using MEDLINE (January 1966 to July 1991), SCISEARCH, manual review of reference lists, and personal contact with more than 30 international experts. Studies of COPD, lung function, emphysema, chronic bronchitis, or mortality in workers exposed to nonorganic dust were retrieved. Studies were included if dust exposure was measured quantitatively, and a quantitative relationship between dust exposure and one of the outcomes of interest was calculated while controlling at least for smoking and age. Methodological rigor was assessed, and data regarding the study populations, prognostic factors, and outcomes were extracted independently by two reviewers. Thirteen reports derived from four cohorts of workers met our inclusion criteria. Three of the cohorts were of coal miners and one was of gold miners. All of the studies found a statistically significant association between loss of lung function and cumulative respirable dust exposure. It was estimated that 80 (95% CI, 34 to 137) of 1,000 nonsmoking coal miners with a cumulative respirable dust exposure of 122.5 gh/m3 (considered equivalent to 35 years of work with a mean respirable dust level of 2 mg/m3) could be expected to develop a clinically important (> 20%) loss of FEV1 attributable to dust. Among 1,000 smoking miners the comparable estimate was 66 (95% CI, 49 to 84). The risk of a clinically important loss of lung function attributable to dust among nonsmoking gold miners was estimated to be three times as large as for coal miners at less than one fifth of the cumulative respirable dust exposure (21.3 gh/m3), the maximal exposure observed among the cohort of gold miners. We conclude that occupational dust is an important cause of COPD, and the risk appears to be greater for gold miners than for coal miners. One possible explanation of the greater risk among gold miners is the higher silica content in gold mine dust.

Bronchitis↗
PubMed1991

Workplace ergonomic factors and the development of musculoskeletal disorders of the neck and upper limbs: a meta-analysis.

In the past 10 years there has been growing awareness among occupational health professionals worldwide of the large burden of illness associated with musculoskeletal disorders of the neck and upper limbs. It has been suggested that these disorders are associated with highly repetitive work and are due, at least in part, to ergonomic factors. This review examines the epidemiologic evidence of the relationship between workplace ergonomic factors such as repetition, force, static muscle loading, and extreme joint position and the development of muscle, tendon, and nerve entrapment disorders of the neck and upper limbs of exposed workers. An extensive search for relevant studies was undertaken. Of 54 potentially relevant studies identified, three met the a priori inclusion criteria. The validity of these studies was assessed, and one study was found to have major flaws. Criteria to demonstrate causality were also applied and were met in the most rigorously conducted study. When the results of these studies are compared and aggregated where appropriate, they provide strong evidence of a causal relationship between repetitive, forceful work and the development of musculoskeletal disorders of the tendons and tendon sheaths in the hands and wrists and nerve entrapment of the median nerve at the carpal tunnel. The comparison of exposed to controls for hand/wrist tendinitis gives an unadjusted common odds ratio of 9.1 (95% CI 4.9-16.2). The adjusted odds ratio for carpal tunnel syndrome is 15.5 (95% CI 1.7-141.5) based on the most rigorous study.

Activities of Daily Living↗