Positive association between serum silicon levels and bone mineral density in female rats following oral silicon supplementation with monomethylsilanetriol.

UNLABELLED: Observational (epidemiological) studies suggest the positive association between dietary silicon intake and bone mineral density may be mediated by circulating estradiol level. Here, we report the results of a silicon supplementation study in rats that strongly support these observations and suggest an interaction between silicon and estradiol. INTRODUCTION: Epidemiological studies report strong positive associations between dietary silicon (Si) intake and bone mineral density (BMD) in premenopausal women and indicate that the association may be mediated by estradiol. We have tested this possibility in a mixed-gender rodent intervention study. METHODS: Tissue samples were obtained from three groups of 20-week-old Sprague Dawley rats (five males and five females per group) that had been supplemented ad libitum for 90 days in their drinking water with (i) <0.1 mg Si/L (vehicle control), (ii) 115 mg Si/L (moderate dose) or (iii) 575 mg Si/L (high dose). All rats received conventional laboratory feed, whilst supplemental Si was in the form of monomethylsilanetriol, increasing dietary Si intakes by 18 and 99 %, for the moderate- and high-dose groups, respectively. RESULTS: Fasting serum and tissue Si concentrations were increased with Si supplementation (p < 0.05), regardless of gender. However, only for female rats was there (i) a trend for a dose-responsive increase in serum osteocalcin concentration with Si intervention and (ii) strong significant associations between serum Si concentrations and measures of bone quality (p < 0.01). Correlations were weaker or insignificant for tibia Si levels and absent for other serum or tibia elemental concentrations and bone quality measures. CONCLUSIONS: Our findings support the epidemiological observations that dietary Si positively impacts BMD in younger females, and this may be due to a Si-estradiol interaction. Moreover, these data suggest that the Si effect is mediated systemically, rather than through its incorporation into bone

Access to recreational physical activities by car and bus : an assessment of socio-spatial inequalities in mainland Scotland

Obesity and other chronic conditions linked with low levels of physical activity (PA) are associated with deprivation. One reason for this could be that it is more difficult for low-income groups to access recreational PA facilities such as swimming pools and sports centres than high-income groups. In this paper, we explore the distribution of access to PA facilities by car and bus across mainland Scotland by income deprivation at datazone level. GIS car and bus networks were created to determine the number of PA facilities accessible within travel times of 10, 20 and 30 minutes. Multilevel negative binomial regression models were then used to investigate the distribution of the number of accessible facilities, adjusting for datazone population size and local authority. Access to PA facilities by car was significantly (p<0.01) higher for the most affluent quintile of area-based income deprivation than for most other quintiles in small towns and all other quintiles in rural areas. Accessibility by bus was significantly lower for the most affluent quintile than for other quintiles in urban areas and small towns, but not in rural areas. Overall, we found that the most disadvantaged groups were those without access to a car and living in the most affluent areas or in rural areas

The importance of loading frequency, rate and vibration for enhancing bone adaptation and implant osseointegration

Mechanical loading is one of the key factors that influence bone mass and the osseointegration of bone-anchored implants. From a clinical point of view, mechanical stimulation may be used to enhance bone strength and implant osseointegration. Among the many loading parameters that influence the response to mechanical loading, the effects of loading frequency and rate have been investigated in many studies. In this paper the most relevant animal studies that have addressed the effect of loading frequency, rate, and vibration on either bone adaptation or implant osseointegration are systematically reviewed. Apparently contradictory results are discussed and interpreted within the context of mechanotransduction and mechanoregulation of bone. A combined experimental and computational approach is suggested to address some of the remaining research questions

How morphology predicts mechanical properties of trabecular structures depends on intra-specimen trabecular thickness variations

Two observations underlie this work. First, that the architecture of trabecular bone can accurately predict the mechanical stiffness characteristics of bone specimens when considering the combination of volume fraction and fabric, which is a measure of architectural anisotropy. Second, that the same morphological measures could not accurately predict the mechanical properties of porous structures in general. We hypothesize that this discrepancy can be explained by the special nature of trabecular bone as a structure in remodeling equilibrium relative to the external loads. We tested this hypothesis using a generic model of trabecular bone. Five series of 153 different architectures were created with this model. Each architecture was subjected to morphological analysis, and four different fabric measures were calculated to evaluate their effectiveness in characterizing the architecture. Relationships were determined relating morphology to the elastic constants. The quality of these relationships was tested by correlating the predicted elastic constants with those determined from finite element analysis. We found that the four fabric measures used could estimate the mechanical properties almost equally well. So the suggestion that fabric measures based on trabecular bone volume better represent the architecture than mean intercept length could not be affirmed. We conclude that for structures with equally sized elliptical voids the mechanical properties can be predicted well only if trabecular thickness variations within each structure are limited. These structures closely resemble previously developed models of trabecular bone. Furthermore, they are stiff in the principal fabric direction, hence, according to Cowin (J. Biomech. Eng. (108) (1986) 83), they are in remodeling equilibrium. These structures are also stiff over a large range of loading orientations, hence, are relatively insensitive to deviations in direction of loading

Effects of mechanical forces on maintenance and adaptation of form in trabecular bone

The architecture of trabecular bone, the porous bone found in the spine and at articulating joints, provides the requirements for optimal load transfer, by pairing suitable strength and stiffness to minimal weight according to rules of mathematical design. But, as it is unlikely that the architecture is fully pre-programmed in the genes, how are the bone cells informed about these rules, which so obviously dictate architecture? A relationship exists between bone architecture and mechanical usage while strenuous exercise increases bone mass9, disuse, as in microgravity and inactivity, reduces it. Bone resorption cells (osteoclasts) and bone formation cells (osteoblasts) normally balance bone mass in a coupled homeostatic process of remodelling, which renews some 25% of trabecular bone volume per year. Here we present a computational model of the metabolic process in bone that confirms that cell coupling is governed by feedback from mechanical load transfer.This model can explain the emergence and maintenance of trabecular architecture as an optimal mechanical structure, as well as its adaptation to alternative external loads

Evaluation of an in situ formed synthetic hydrogel as a biodegradable membrane for guided bone regeneration

The aim of the present study was to test whether or not the application of an in situ formed synthetic hydrogel made of polyethylene glycol (PEG) used as a biodegradable membrane for guided bone regeneration will result in the same amount of bone regeneration as with the use of an expanded polytetrafluoro- ethylene (ePTFE) membrane. In eight New Zealand White rabbits, four evenly distributed 6 mm diameter defects were drilled into the calvarial bone. Three treatment modalities were evenly distributed among the 32 defects: hydroxyapatite (HA)/tricalciumphosphate (TCP) granules covered at the outer and inner surface with a PEG membrane (test), HA/TCP granules covered at the outer and inner surface with an ePTFE membrane (positive control) and HA/ TCP granules alone without membranes (negative control). After 4 weeks, the animals were sacrificed and the calvarial bones were removed. The area fraction of newly formed bone was determined by histomorphometrical analysis of the vertical sections from the middle of the defect and by micro-computed tomography of the entire defect. Multiple regression analysis (SAS® GLM) was used to model the amount of new bone formation. The quantitative histomorphometric analysis clearly revealed higher values of newly formed bone for the two membrane groups compared with the negative control group. The average area fractions of newly formed bone measured within the former defect amounted to 20.3 ± 9.5% for the PEG membrane, 18.9 ± 9.9% for the ePTFE membrane, and 7.3 ± 5.3% for the sites with no membrane. The micro-computed tomography also showed higher values of new bone formation for the PEG and for the ePTFE groups compared with the negative control group. The GLM revealed a highly significant effect of the treatment on the amount of bone formation (P = 0.0048). The values for the negative control group were significantly lower than the ones found in the PEG membrane group (P = 0.0017), whereas the ePTFE membrane group showed no significant difference from the PEG membrane group. It is concluded that the PEG membrane can be used successfully as a biodegradable barrier membrane in the treatment of non-critical-size defects in the rabbit skull, and leads to similar amounts of bone regeneration as an ePTFE membrane. Copyright © Blackwell Munksgaard 2006.link_to_subscribed_fulltex

Subject-specific bone loading estimation in the human distal radius

High-resolution in vivo bone micro-architecture assessment, as possible now for the distal forearm, in combination with bone remodelling simulation algorithms could, eventually, predict patient-specific bone morphology changes. To simulate load-adaptive bone remodelling, however, physiological loading conditions must be defined. In this paper we test a previously developed algorithm to estimate such physiological loading conditions from the bone micro-architecture. The aims of this study were to investigate if realistic boundary forces and moments are predicted for the scanned distal radius section and how these predicted forces and moments should be distributed to the scanned section in order to obtain a load transfer similar to that in situ. Images at in vivo resolution were generated for the clinically measured section of nine distal radius cadaver bones, converted to micro-finite element models and used for load estimation. Models of the full distal radius were created to analyse tissue loading distributions of the sections in situ. It was found that predicted forces and moments at the boundaries of the scanned region varied considerably but, when translated to equivalent radiocarpal joint forces, agreed well with values reported in the literature. Bone tissue loading distribution was in best agreement with in situ distributions when loading was applied to an extra layer of material at both ends of the clinical scan region. The agreement of the predicted loading to previous studies and the wide range of predicted loading values indicate that subject-specific bone loading estimation is possible and necessary