Trabecular bone volume

K. Kose, Y. Matsuda, T. Kurimoto, S. Hashimoto, Y. Yamazaki, T. Haishi, S. Utsuzawa, H. Yoshioka, S. Okada, M. Add, T. Tsuzaki 2004, (Development of a compact MRI system for trabecular bone volume fraction measurements), Magn. Reson. Med. 52, 440—444. 

Chow J, Tobias JH, Colston KW, Chambers TJ (1992) Estrogen maintains trabecular bone volume in rats not only by suppression of bone resorption but also by stimulation of bone formation. J Clin Invest 89 74-78... 

Thirty-seven weeks after ovariectomy, marked decreases of 73% (p <. 01) and 77% (p <. 01) in trabecular bone volume and trabecular bone number (data not shown), respectively, were observed at 1 to 5 mm of the growth plate metaphyseal junction of the proximal tibia. Simultaneously, a marked increase in trabecular bone separation from a control value in intact rats of 262 19 to 1486 236 pm (p <. 01) was observed in OVX animals. Treatment with 1 mg/kg of EM-800 and raloxifene resulted in 68% (p<. 01) and 64% (p <. 01) reversals, respectively, of the decrease in trabecular bone volume caused by ovariectomy. In fact, treatment with EM-800 and raloxifene at the daily 1 mg/kg dose increased trabecular bone volume of the proximal tibia from a control value of 5.8 0.9% in OVX animals to 16.4 0.4% and 15.8 1.0%, respectively. These stimulatory effects are not statistically different from the 53% reversal achieved with E2. At the lowest dose used (0.01 mg/kg), EM-800 already reversed by 34% (p <. 01) the elfect of OVX whereas raloxifene had no detectable effect. The administration of 0.1 mg/kg of EM-800 and raloxifene, on the other hand, resulted in 40% (p <. 01) and 24% (p <. 05) reversals, respectively, of the decrease in trabecular bone volume caused by OVX. 

Figure 27 (see color insert) illustrates the prevention of trabecular bone volume in the proximal tibial metaphysis induced by EM-800 and raloxifene in ovariectomized treated animals compared with OVX controls (Fig. 27B). The administration of 0.01 mg/kg of EM-800 (Fig. 27D) already prevented by 52% the OVX-induced osteopenia, whereas raloxifene had no detectable elfect at the same dose (Fig. 27F). Treatment...

Bone is divided into trabecular and cortical components, with each further divided into surface bone, bone volume, and bone cavity (marrow compartment). Deposition of americium is assumed to occur from plasma directly to bone surfaces, whereas elimination from bone occurs by transfer from the bone surface or volume to the marrow cavity, and then from the marrow cavity to plasma (Figure 3-6). Transfers of americium within the cortical or trabecular bone compartments are modeled based on assumptions about rates of bone formation and resorption, which are assumed to be vary with age, but are equal within a given age group (Leggett et al. 1982). Movement of americium to the marrow compartment is determined by the bone resorption rate, whereas, movement from the bone surface to the bone volume is assumed to occur by burial of surface deposits with new bone and is determined by the bone formation rate. During growth, bone formation and resorption are assumed to occur at different sites within bone therefore, the rate of removal of americium from the bone surface is approximated by the sum of the bone resorption rate (represented in the model by the movement of americium to the marrow compartment) and the rate of bone... 

S. Overgaard, K. Soballe, M. Lind, C. Biinger, Resorption of hydroxyapatite and fluorapatite coatings in man. An experimental study in trabecular bone, J. Bone Joint Surg. (British Volume) 79 (1997) 654-659. 

The main functions of bone are (1) mechanical, for locomotion (2) protective, for organs and (3) metabolic, as a reserve for minerals, especially calcium and phosphate. Bones are composed of cortical and trabecular bone. Cortical (compact) bone is 80% to 90% mineralized by volume and constitutes 80% of the skeleton. Its function is primarily mechanical and protective. Trabecular bone constitutes the remaining 20% of the skeleton. Trabecular (cancellous or spongy) bone, which is 15% to 25% mineralized, is more metabolicaUy active. 

Strontium distributes relatively uniformly within the bone volume where it exchanges with calcium in hydroxyapatite (see Section 3.5.1), although small differences in the calcium and strontium distributions within bone have been reported. The Sr Ca concentration ratio in bone increases with age from approximately 0.3 mg strontium/g Ca at birth to a value of 0.5 in adults (Papworth and Vannart 1984 Tanaka et al. 1981). The Sr Ca ratio in bone also has been shown to vary with the bone type ratios in cortical bone were approximately 10-20% higher than in trabecular bone (Tanaka et al. 1981). 

The skeleton is divided into cortical and trabecular regions, and each of these is subdivided into bone surfaces, bone volume, and bone marrow. Some 70% of the thorium reaching the blood is assigned initially to bone surfaces and is subsequently transferred to bone marrow by bone resorption, or to bone volume by bone formation. The removal half-time from bone marrow to blood is assumed to be 0.25 years, and is redistributed in the same pattern as the original input to blood. 

The distinction between cortical and trabecular bone is most easily made based on porosity. Cortical bone can be defined as bone tissue that has a porosity P of less than about 30 percent or, equivalently, a volume fraction Vf of greater than about 0.70 (V = 1 — P). Volume fraction is the ratio of the volume of actual bone tissue to the bulk volume of the specimen. In the field of bone mechanics, porosity measures usually ignore the presence of lacunae and canaliculi. Porosity of adult... 

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... 

FIGURE 8J Three-dimensional reconstructions of trabecular bone from the (a) bovine proximal tibia, (b) human proximal tibia, (c) human femoral neck, (d) human vertebra. Each volume is 3 X 3 x 1 mm . From Ref. 142.)... 

TCP, calcium sulfate, and HA can be inserted into a defect in the cortical or trabecular bone in the form of pellets or particles. The high surface-to-volume ratios of these implants, used in areas where immediate structural support is maintained through remaining bone or fracture fixation, allows for more rapid integration and remodeling of the material. The calcium sulfate formulation has been shown to resorb in only 6 to 8 weeks (Ladd and Pliam, 1999). 

The percent volume of water, inorganic, and organic components for hydrated trabeculae have been reported at 27%, 38%, and 35%, respectively [11], although the precise values depend on anatomic site, age, and health. Based on reported wet, dry, and ash apparent densities for specimens of defatted human lumbar spine trabecular bone [4], the percentage weights of the inorganic, organic, and water components for this tissue can be calculated at approximately 54%, 26%, and 20%, respectively. 

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