Trabecular bone density

Skeleton Decreased trabecular bone density Rat ICI164384 (van Bezooijen et al. 1998)... 

Stendig-Lindberg G, Tepper R and Leighter I (1993) Trabecular bone density in a two year controlled trial of peroral magnesium in osteoporosis. 

Typically, mean values of apparent density of hydrated cortical bone are about 1.85 g/cm , and this does not vary much across anatomic sites or species. By contrast, the average apparent density of trabecular bone depends very much on anatomic site. It is as low as 0.10 g/cm for the spine, about 0.30 g/cnP for the human tibia, and up to about 0.60 g/caP for the load-bearing portions of the proximal femur." After skeletal maturity (around ages 25 to 30), trabecular bone density decreases steadily with aging, at a rate of about 6 percent per decade. ... 

In a small cross-sectional study, bone mineral density was studied in 20 prepubertal asthmatic patients treated with moderate to high doses of inhaled glucocorticoids (under 400 micrograms/day beclomethasone or budesonide or over 200 micrograms/day fluticasone) (114). Volumetric trabecular bone mineral density of the lumbar spine and distal radius were measured using dual energy X-ray absorptiometry and were within the reference ranges. 

Osteoporosis, trabecular bone being most affected, has been regularly observed in both sexes with chronic gonadorelin agonist treatment (48), and the duration of therapy for prostate cancer is inversely related to bone mineral density (49,50). Intravenous pamidronate may prevent bone loss in these patients (51,52). 

Although glucocorticoids can cause changes in trabecular microarchitecture, loss of bone (reduced bone density) seems to be the major determinant of osteoporosis (184). 

Fluoride is a potent stimulator of trabecular bone formation. Sodium monofluorophosphate was given to 48 patients with osteoporosis due to glucocorticoids (more than 10 mg of prednisone equivalents/day). Patients were randomly allocated to 1 g of calcium carbonate (control) or 200 mg of sodium monofluorophosphate plus 1 g of calcium carbonate for 18 months. At the end of the study lumbar spine bone density had increased by 7.8% in the fluoride group versus 3.3% in the controls. There were no changes in femoral neck density (SEDA-20, 376) (222). 

Furthermore, there is evidence that it is disease activity rather than methotrexate that accounts for changes in bone mass (89). This 2-year longitudinal study involved 22 patients taking methotrexate and 18 patients taking other DMARDs it was strictly controlled for the use of glucocorticoids. There were significant and equal reductions in trabecular bone mineral density in both groups. Bone loss was most marked in patients with active disease. 

Ratios of bulk metals to ultratrace metals have been used by some workers to gain insight into the altered relationship of metal concentration in the aged (US), For example, the ratio of calcium to zinc in both trabecular and cortical bone has been found to be inversely proportional to the age of the subject. In patients with osteoporesis, minerals in general are quantitatively reduced although they remain the same qualitatively, meaning that bone density decreases as the subject advances in age. 

Two other common measures of bone density in biomechanical studies are termed tissue and apparent densities. Tissue density p i is defined as the ratio of mass to volume of the actual bone tissue. It is similar for cortical and trabecular bone, varies little in adult humans, and is about 2.0 g/cm. Apparent density p pp is defined as the ratio of the mass of bone tissue to the bulk volume of... 

Interestingly, the failure (yield and ultimate) strains of human trabecular bone have only a weak dependence, if any, on apparent density and modulus." - - - A recent study designed to test for intersite differences found that yield strains were approximately uniform within anatomic sites, with standard deviations on the order of one-tenth the mean value, but mean values could vary across sites" (Fig. 8.13). Thus, for analysis purposes, yield strains can be considered constant wiAin sites but heterogeneous across sites. Regardless of anatomic site, however, yield stains are higher in compression than in tension." Ultimate strains are typically in the range of 1.0 to 2.5 percent. Evidence from experiment on bovine bone indicates that yield strains are also isotropic - despite substantial anisotropy of modulus and strength. 

Differences in the predictive power between the various linear and power laws are usually negligible within a singie anatomic site because the range of apparent density exhibited by trabecular bone is less than 1 order of magnitude. 

TABLE 8.4 Power-Law Regressions Between Modulus E (in MPa) and Apparent Density p (in g/cm ) for Human Trabecular Bone Specimens from a Range of Anatomic Sites... 

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