Density cortical bone

Cheng S, Tylavsky F, Kroger H et al. (2003) Association of low 25-hydroxyvitamin D concentrations with elevated parathyroid hormone concentrations and low cortical bone density in early pubertal and prepubertal Finnish girls. American Journal of Clinical Nutrition 78 485-492. 

The geometry and structure of a bone consist of a mineralised tissue populated with cells. This bone tissue has two distinct structural forms dense cortical and lattice-like cancellous bone, see Figure 7.2(a). Cortical bone is a nearly transversely isotropic material, made up of osteons, longitudinal cylinders of bone centred around blood vessels. Cancellous bone is an orthotropic material, with a porous architecture formed by individual struts or trabeculae. This high surface area structure represents only 20 per cent of the skeletal mass but has 50 per cent of the metabolic activity. The density of cancellous bone varies significantly, and its mechanical behaviour is influenced by density and architecture. The elastic modulus and strength of both tissue structures are functions of the apparent density. 

The mechanical properties of cancellous bone are dependent upon the bone density and porosity, and the strength and modulus are therefore much lower than those for cortical bone. The axial and compressive strength are proportional to the square of the bone density, and moduli can range from 1 to 3 GPa. 

Bone mineral density was measured after 7.4 months in 49 asthmatic children, 38 of whom took inhaled beclomethasone, average daily dose 276 micrograms, and 11 sodium cromoglicate, average daily dose 30 mg (121). Children who had used beclomethasone had grown as much as those who used sodium cromoglicate. Trabecular and cortical bone mineral density in the proximal forearm and lumbar spine increased to the same extent in both groups. 

The high brilliance X-ray diffraction pattern of the new biomaterial was compared with that of the cortical bone of a rabbit and also sintered HAP. The dahllite-based biomaterial had a diffraction pattern very similar to that of the bone, while sintered HAP was highly crystalline. The crystallite sizes of bone as well as their biomaterial were very similar, equal to an average size of 5 nm. Unlike bone, however, the crystallites in the biomaterial oriented unidirectionally because they were rapidly formed in the absence of an organic matrix. The density of the new biomaterial was found to be 1.3 g cm , and the average pore diameter was 30 nm. These measurements indicate that both crystallite size and the porosity are at the nanoscale and result in broad peaks in the X-ray diffraction pattern. Bigger crystallites would have yielded sharper peaks in the sintered HAP. 

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. 

The values of indices for both cortical width and bone mineral content were significantly lower in itai-itai disease patients than the Cd-exposed subjects. The Cd-exposed women also showed a decrease in bone density compared with the non-exposed subjects. A significant decrease in bone density was also observed between Cd-exposed men and the non-exposed subjects, although the difference was not as distinct as in women. In other Cd-polluted areas such as the Jinzu River basin or Tsushima Island, a decrease in bone density in Cd-exposed subjects has also been reported using the same method [82, 83]. 

There are two basic structural types of bone cancellous (trabecular, spongy) and cortical (dense) bones. Cancellous bone matter is less dense than that of cortical bone and is found across the ends of the long bones. Owing to its lower density, cancellous bone has also a much lower modulus of elasticity but higher strain-to-failure rate compared to cortical bone (Table 3.1). Bone has higher moduli of elasticity than soft connective tissues, such as tendons and ligaments. The difference in stiffness (elastic modulus) between the various types of connective tissues ensures a smooth gradient in mechanical stress across a bone, between bones and between muscles and bones (Hench, 2014). 

In general, peak bone mass occurs between 30 and 40 years of age (3,6) and is dependent on genetic factors as well as proper intake of calcium, maintenance of quality nutrition, and participation in weight-bearing exercise (6). Thereafter, peak bone mass progressively declines at the rate of 0.3 to 0.5% of cortical bone per year (3). After menopause, bone loss is accelerated (2% per year in the spine) (6) for a period of 5 to 10 years because of the loss of estrogen. This can result in up to a 30% decrease in bone mineral density. 

Because raloxifene only reduces the risk of vertebral fracture, there is a need to identify agents that are effective at multiple skeletal sites with minimal side effects. The novel SERM HMR-3339 improves bone mineral density in adult ovariectomized rats at a variety of skeletal sites (e.g., lumbar spine, tibia, and femur), including those sites composed of cortical bone (118,119). An additional benefit afforded by HMR-3339 is a reduction in total... 

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... 

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. ... 

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