Reduction in bone mass

Osteoporosis is a disease characterized by a reduction in bone mass and a deterioration in bone microarchitecture, which leads to enhanced fragility. This is a very common disorder, and it is becoming more common with the increase of life expectancy thus, it is a major public health issue. Osteoporosis is caused by an increase in bone loss and at the same time a decrease in bone formation. With increasing age, bone formation is slowed down, especially in women after the menopause, although it is also seen sometimes in men, usually aged over 70 years (senile osteoporosis). 

Gadolinium-153 is widely used in medicine to detect osteoporosis, the reduction in bone mass that often accompanies aging. Bone density is determined by a scanning device that compares how much of the X rays and gamma rays produced by the decay of gadolinium-153 is absorbed by a bone. The scans shown compare a dense bone with one that has lost a great deal of mineral matter. 

O.stcoporosis is characterized by a reduction in bone mass per unit volume. The composition of the matrix is essentially nonnal. but there is just less of it. The cortical areas of bones are thinner than nomial and the trabeculae are smaller and le.ss extensive (Fig. I). Both sexes show a gradual bone loss throughout life but women lo.se bone rapidly in the postmenopausal years. This is called primary osteoporosis and is of unknown aetiology. 

Osteoporosis is a major cause of morbidity and mortality in the elderly. It is characterized by a reduction in bone mass per unit volume. 

Involutional (primary) osteoporosis is the manifestation of a metabolic bone disease in which the amount of normally mineralized bone matrix in affected patients has been reduced to a level below that of the normal population of the same age and sex. The disease is certainly of multifactorial origin, since genetic (Seeman etal. 1989), mechanical (e.g.. Frost 1988), nutritional (e.g., Hegsted 1986), and hormonal factors (e.g., Melton and Riggs 1988) can cause the severe impairment of the bone remodeling process (Eriksen etal. 1994) which underlies the observed reduction in bone mass and microarchitectural deterioration of bone tissue that lead to an increased risk of fractures at typical sites of the skeleton (for a definition, see Anonymous 1993)... 

Similarly, when abnormal underloading causes bone strain to be less than the lower set-point, the Mechanostat activates and recruits cellular activity for bone resorption. The reduction in bone mass makes the skeleton more fragile, causing bone strain to increase. 

DEFICIENCY Deficiency causes hypocalcemia and hypophosphatemia, with resultant rickets (bending with poor calcification of developing bone in riuldren) or osteomalacia (decalcification and sofietring of bones in adults). In both of these there is impaired mineralization. These should be distinguished from another condition, osteoporosis, in which there is reductioii in bone mass as a whole, rather than select reduction of the mineral content. 

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. 

Musculoskeletal Bone area and bone mineral content in lumbar spine, hip, and whole body were measured with dual radiograph absorptiometry in 59 children aged 13-15 who had been bom preterm and randomly assigned standard or aluminium-depleted parenteral nutrition solutions during the neonatal period. Those who had been randomly assigned to standard parenteral nutrition solutions had lower lumbar spine bone mineral content, apparently explained by a reduction in bone size. In nonrandomized analyses, children who were exposed as neonates to aluminium above the median (55 micrograms/kg) had lower hip bone mineral content, independent of bone or body size. The authors concluded that neonates who are exposed to parenteral aluminium may have reduced lumbar spine and hip bone mass during adolescence, potential risk factors for later osteoporosis, and hip fracture. 

Osteoporosis is a consequence of the reduction of skeletal mass caused by an imbalance between bone resorption and bone formation. The loss of gonadal function and aging are the two main factors that contribute to the development of osteoporosis. Around the fourth or fifth decade of life, men and women lose bone at a rate of 0.3-0.5% per year. After menopause, the rate of bone loss increases to 10% a year (Nordin et al. 1990 Riggs et al. 1986,1998). The bone loss due to estrogen withdrawal is associated with increments in both bone resorption as well as in bone formation, with the former exceeding the latter. This indicates the birth of new BMUs or an increase in the lifespan of cur-... 

The bone becomes depleted of calcium salts when the urine is acidic over a relatively long period. This was shown by Goto (17) who fed rabbits large doses of hydrochloric acid. He then showed that urinary calcium loss occurred in concert with a marked reduction in mass of the skeletal system, and also that the total non-fat dry weight of bone decreased,implying a loss of bone matrix. A dose-dependent, dietary acid induced loss of labelled calcium from rat bone has been reported by Thorn and his coworkers (18). They demonstrated that in response to graded doses of ascorbic acid, cells in tissue culture, and bones in whole animals fed such doses were depleted of the labelled calcium. 

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