Bones microarchitecture

Hildebrand T., Ruegsegger P. Quantifieation of bone microarchitecture with the structure model index. CMBBE, v.l, 15-23, 1997. 

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). 

Bone tissue is constantly being renewed by the concerted action of osteoblasts and osteoclasts. Bone remodeling has two main phases a resorption phase consisting in the removal of old bone by osteoclasts, and a later phase of new bone formation driven by osteoblasts [6], Thus, the activity of osteoblasts and osteoclasts determines bone mass, bone geometry, bone quality, and, subsequently, bone strength [7, 8]. Osteoporosis is a prevalent disorder consisting in decreased bone mass and/or abnormal bone microarchitecture that impairs bone strength and increases the risk of fracture. Therefore, patients with osteoporosis may suffer fractures as a result of minor trauma, or even in the absence of trauma. The most common osteoporotic fractures are those of the vertebral bodies, the hip, the wrist, the shoulder, and the pelvis. 

Figure 17.9 Schematic of bone microarchitecture. (a) Three-dimensional bone sector showing tissue microstnicture progression from outer periosteum to inner trabeculae, osteon assembly, and enclosed vasculature, (b) Schematic of bone remodeling, as a result of continuous bone resorption by osteoclasts and new bone formation by osteoblasts.

Postmenopausal osteoporosis is a condition that affects millions of women and is characterized by low bone mass with microarchitectural deterioration of bone tissue that can... 

A variety of diseases can affect bone and its structure. Paget s disease, for example, is a disorder arising from abnormal osteoclasts, characterized by exeessive bone resorption followed by replacement of the normal mineralized bone with structurally weak, poorly mineralized tissue. However, the most important bone disease is osteoporosis. This is a skeletal bone disease characterized hy microarchitectural deterioration of bony tissue and loss of bone mass, yielding increased susceptibility to bone fracture and bone fragility. In the United States, osteoporosis results in 1.5 million hone fractures annually, with 250,000 of these being hip fractures that sometimes ultimately culminate in patient death. There is a variety of therapies for the prevention and treatment of osteoporosis. 

Fig. 1. Microarchitecture and structural classifications of physiological bone, (a) Schematic of microscopic and structural classifications of bone. (Redrawn and adapted from Kaplan et al., 1994.) (b) Schematc of the microarchitecture of the femur. (Redrawn and adapted from Keaveny and Hayes, 1993, and Fung, 1993.)...

The other microarchitectural form of bone, lamellar bone, actively replaces maturing woven bone and, consequently, contains up to 100 times more mineralized matrix or hydroxyapatite these hydroxyapatite crystals... 

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

Metabolic bone diseases result from a partial uncoupling or imbalance between bone resorption and formation. Decreased bone mass, or osteopenia, is more common than abnormal increases of bone mass. The most prevalent metabolic bone diseases are osteoporosis, osteomalacia and rickets, and renal osteodystrophy. Osteoporosis, the most prevalent metabolic bone disease in developed countries, is characterized by loss of bone mass, microarchitectural deterioration of bone tissue, and increased risk of fracture. Rickets and osteomalacia, which are more common in the less-developed countries, are characterized by defective mineralization of bone matrix. Renal osteodystrophy is a complex condition that develops in response to abnormalities of the endocrine and excretory functions of the kidneys. These three metabolic bone diseases and Paget s disease, a localized bone disease, are discussed below followed by laboratory markers of bone metabolism. 

An estimated 75 million people are affected by osteoporosis to some degree in the United States, Europe, and Japan. Osteoporosis is a systematic skeletal disease characterized by bone mass and microarchitectural deterioration with a consequent increase in bone fragility and susceptibility to fracture. Operationally, osteoporosis can be defined as a certain level of bone mineral density. The definition of osteoporosis is somewhat arbitrary and is based on epidemiological data relating fracture incidence to bone mass. Uncertainty also is introduced due to variability in bone densitometry measurements. Other clinical measures to assess the skeleton include collagen cross-links (measure of bone resorption) and levels of bone-specific alkaline phosphatase and osteocalcin (bone formation). A list of biochemical markers of bone remodeling is provided in Table 37-3. Measurement of total serum alkaline phosphatase level and urinary hydroxyproline or calcium levels is of limited value. 

Bone resorption increases with age, but changes in bone formation are not observed consistently. Increased osteocyte apoptosis may decrease responses to mechanical strain and hinder bone repair. Cortical porosity from years of remodeling and decreased trabecular connectivity, particularly of horizontal struts, promotes microarchitectural deterioration of bone that is not always reflected in BMD. Aging also increases fracture risk in other ways that are independent of BMD. 

Osteoporosis—(1) Reduced bone mass associated with architectural deterioration of the skeleton and increased risk for fracture. (2) A chronic, progressive disease characterized by very low bone density (DXA T score <—2.5), microarchitectural deterioration and decreased bone strength, bone fragdity, and a consequent increase in fracture risk. 

Armamento-Villareal, R., Sheikh, S., Nawaz, A., Napoli, N., Mueller, C., Halstead, L.R., Brodt, M.D., Silva, M.J., Galbiati, E., Caruso, P.L., Civelli, M. and Civitelli, R. (2005) A new selective estrogen receptor modulator, CHF 4227.01, preserves bone mass and microarchitecture in ovariectomized rats. Journal of Bone and Mineral Research, 20, 2178-2188. 

Osteoporosis is a systemic skeletal disease characterized by a low bone mass and microarchitectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture. It is a major cause of mortality, morbidity, and medical expense worldwide. 

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)... 

Osteoporosis is a condition of low bone mass and microarchitectural disruption that results in fractures with minimal trauma. Characteristic sites of fracture include vertebral bodies, the distal radius, and the proximal femur, but osteoporotic individuals have generalized skeletal fragility, and fractures at sites such as ribs and long bones also occur. Fracture risk increases exponentially with age, related both to decreased bone density and to factors such as decreased muscle strength and increased risk of falls. 

Osteoporosis is a skeletal disease that is characterized by loss of bone mass as well as microarchitectural deterioration of the bone tissue. This disease is associated with increased bone fragility and susceptibility to fracture. It is a condition that is characterized not by inadequate bone formation but, rather, by a deficiency in the production of well-mineralized bone mass. Whereas no medical cause typically is evident in primary osteoporosis (3), secondary osteoporosis classically stems from medical illness or medication use. There are two types of primary adult osteoporosis, type I, or postmenopausal, and type II, or senile (Table 35.1). In type I osteoporosis, there is an accelerated rate of bone loss via enhanced resorption at the onset of menopause. In this form of the disease, the loss of trabecular bone is threefold greater than the loss of cortical bone. This disproportionate loss of bone mass is the primary cause of the vertebral crush fractures and the wrist and ankle fractures experienced by postmenopausal women. In type II osteoporosis, which is associated with aging, the degree of bone loss is similar in both trabecular and cortical bone (5) and is caused by decreased bone formation by the osteoblasts. 

Whang K, Healy E, Elenz DR (1999) Engineering bone regeneration with bioabsorbable scaffolds with novel microarchitecture. Tissue Eng 5 35-51... 

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