Monte Carlo simulations of electron scattering in bone

Relative changes in the mineralization level within bone can be studied using backscattered electron (BSE) imaging in a scanning electron microscope (SEM). We calculated the size and shape of the volume element studied, choosing conditions which are typical for practical experimental work with polymethylmethacrylate (PMMA)-embedded bone. Absolutely flat surfaces of embedded bone blocks cannot be generated, and a further aim was to examine the effect of the surface topography on the detected BSE signal level. For normal beam incidence, 20 kV, and modeling an annular detector by collecting BSE with take-off angles of between 45 degrees and 75 degrees to the flat sample surface, it was found that the collectable BSE signal intensity peaks for electrons which leave the specimen surface at a radial distance of approximately 1 micron from the beam impact point. The layered structure of the bone generates topographic relief on polishing. Modeling this by a sinusoidal profile of wavelength 5.0 and amplitude 0.5 micron and again for 20 kV, it was found that the signal derived from the troughs is reduced by 14.4% and that from the crests is increased by 17.2%. The two effects may add constructively to generate the frequently observed strong contrast correlating with the distribution of bone lamellae. No net change in mineral packing density would be expected from a change in collagen orientation, and the lamellar contrast observed in practice can be explained solely by the topographic contrast.

Short-term oral phosphate and bone remodeling in beagles

Attempts to increase bone volume in osteoporotic patients are still in the experimental stage. The coherence therapy, proposed by Frost, suggests that the activated bone units can remodel bone matrix in tandem. The cells (i.e., osteoclast and osteoblast which compose the remodeling units) are manipulated through specific medications timed to each of their duration of actions. The current study was to examine the effect of withdrawal of oral phosphate on bone in ovariectomized dogs. The present report demonstrates the capability of short-term oral phosphate to activate bone remodeling in the ovariectomized animal model. Results from biochemical and histomorphometric analyses confirm that remodeling units are activated following the release of parathyroid hormone. This transient scenario inflicts a shift of mineral density distribution in cancellous bone matrix of the iliac crest. Nevertheless, the bone remodeling units appear to be synchronized with each other and thus their resorptive and formative phases should be amenable to further pharmacological manipulation.

Age and disease-related changes in the mineral of bone

Bone mineralization changes with age and disease. The distribution of mineral particles in a given bone (mineralization profile) has been studied using density fractionation as well as microradiography and electron backscattering imaging. The biological determinant of mineralization is the rate of turnover. During rapid growth and periods of high remodeling, mineralization is shifted towards lower mineral density (hypomineralization). During aging and periods of low remodeling, mineralization is shifted towards higher mineral densities (hypermineralization). Chemicals can also influence the mineralization profile of bone. Fluoride induces hypermineralization by stabilizing the apatite lattice and reducing bone mineral solubility, whereas strontium induces hypomineralization by loosening the apatite lattice and increasing bone mineral solubility. Drugs such as bisphosphonates induce hypermineralization by inhibiting resorption and acting as crystal poison. Finally, mineralization can be impaired by defects as in rickets and osteomalacia or made excessive by continuous accretion of mineral without resorption as in osteopetrosis.

Linear calibration of radiographic mineral density using video-digitizing methods

Radiographic images can provide quantitative as well as qualitative information if they are subjected to densitometric analysis. Using modern video-digitizing techniques, such densitometry can be readily accomplished using relatively inexpensive computer systems. However, such analyses are made more difficult by the fact that the density values read from the radiography have a complex, nonlinear relationship to bone mineral content. This article derives the relationship between these variables from the nature of the intermediate physical processes, and presents a simple mathematical method for obtaining a linear calibration function using a step wedge or other standard.

Some effects of basic multicellular unit-based remodelling on photon absorptiometry of trabecular bone

This article offers algorithms and an algebra for estimating effects of bone turnover, remodelling space, undermineralized bone and trabecular surface-to-volume ratio effects on trabecular bone mass estimation by photon absorptiometry. From published histomorphometric data and other evidence the algorithms suggest the amount of mineral in a given bone sample can suggest to absorptiometry an amount of bone that differs from the truth by over 40% in the extreme, and more commonly by 5-15%. They suggest that by reducing a bone's global mineral content high bone turnover causes underestimation of true bone mass. They suggest that by letting mineral return to the remodelling space and undermineralized bone, reduced bone turnover causes apparent gains in bone mass. The commonly suggested 5-15% magnitude of such errors exceeds those assumed in the past. The algorithms suggest that after a challenge to remodelling those bone mineral changes can take from 6 months to over 3 years to reach steady states. Those features could explain why many osteoporosis treatments judged effective from initial absorptiometric evidence failed when used for long periods in patients. Finally the algorithms suggest that a real increase in ideal bone volume can even appear to absorptiometry as no gain or an initial loss, which has already happened in two human experiments.

Estimation of the bone mineral density variation associated with changes in turnover rate

Bone matrix mineral density (BMDn, fraction of maximum) is the mean mineral density of a bone sample comprising moieties of bone of varying ages/mineral densities. A method for calculating BMDn as a function of bone turnover rate is presented. The method is based on a mineralization curve defined by values for mineralization lag time, total mineralization time, and levels of primary and final mineralization. The calculations illustrate that BMDn decreases linearly in direct proportion to increases in bone turnover rate, and that the slope of the line is dependent on the assumptions used to calculate the mineralization curve. BMDn variation is important because it is reflected in whole bone density variation, independent of changes in bone mass, when bone turnover rate is altered.

Effects of B-aminopropionitrile on mineralization during endochondral ossification in chick tibia

Two-week-old white leghorn chicks were fed a diet containing BAPN (0.05%) for three weeks. Thirty-six hours before sacrifice, the controls and BAPN fed chicks were dosed with 35S. The zone of provisional calcification was isolated, and 35S incorporation was estimated by liquid scintillation counting. Alkaline phosphatase and Ca+2-ATPase were biochemically analyzed. Microdensitometry, to assess the level of mineralization, was done on epiphysis and the metaphysis. Morphometry was performed on the various zones of growth plate. 35S incorporation was significantly lower in the bones of BAPN treated chicks as compared to the controls. The enzymatic studies showed a significant inhibition of alkaline phosphatase and Ca+2-ATPase. The microdensitometric studies showed a smaller area of highly mineralized bone in the zones of provisional calcification of the BAPN treated chicks as compared to the controls. Morphometry showed a reduction in the width of the zone of calcification in BAPN treated chicks as compared to the controls. On the basis of the above data, it is suggested that BAPN induced inhibition of mineralization during endochondral ossification may be the result of a lower synthesis of sulfur containing GAG's, the inhibition of enzymes alkaline phosphatase and Ca+2-ATPase and the derangement of cellular zones of the growth plate. The implications of these results lie in the fact that mineralization is dependent on multifactorial control of the microenvironment of bone and cartilage.