Bones cancellous

A bone is classified according to shape as flat, long, short, or irregular. A living bone consists of three layers the periosteum, the hard cortical bone, and the bone marrow or cancellous bone. The periosteum is a thin coUagenous layer, filled with nerves and blood vessels, that suppHes nutrients and removes cell wastes. Because of the extensive nerve supply, normal periosteum is very sensitive. When a bone is broken, the injured nerves send electrochemical neural messages relaying pain to the brain. 

Most bones of the human skeleton are composed of two structurally distinct types of tissue compact (dense) and trabecular (cancellous, spongy) bone. Both types contain the same elements cells ( osteocytes) embedded in a mineralised matrix and connected by small canals ( canaliculi ). In compact bone, which makes up 85% of the skeleton, these components form elongated cylinders of concentric lamellae surrounding a central blood vessel (called osteon or Haversian system). Cancellous bone, in contrast, forms thin,... 

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. 

Figure 7.2. Schematics of bone anatomy (a) the structure of a long bone demonstrating the distribution of the two different tissue structures, cortical and cancellous bone, and (b) the cells present in bone osteoblasts, bone-forming cells found on surfaces osteocytes, bone cells embedded in the mineralised matrix and osteoclasts, bone-removing cells.

Fig. 11.7 Representative stress-strain curve of nano-hybrid PD30Cal5, in comparison with that reported for human cancellous bone.

A representative stress-strain curve of one of the PDMS-CaO-Si02 nano-hybrids is shown in Figure 11.7, in comparison with that reported for human cancellous bone [29]. Unlike the usual brittle ceramics, the nano-hybrid was deformable and showed mechanical properties analogous to those of human cancellous bone. 

There are two types of bone (a) compact or cortical bone and (b) trabecular or cancellous bone. Cortical bone is found principally in the shafts (diaphyses) of long bones. It consists of a number of irregularly spaced overlapping cylindrical units termed Haversian systems. Each consists of a central Haversian canal surrounded by concentric lamellae of bony tissue. Trabecular bone is found principally at the ends of long bones and flat bones. It is composed of a meshwork of trabeculae within which... 

Bourrin S, Ammann P, Bonjour J-P, Rizzoli R (2002) Recovery of proximal tibia bone mineral density and strength but not cancellous bone architecture, after longterm bisphosphonate or selective estrogen receptor modulator in aged rats. Bone 30 195-200... 

Gallagher A, Chambers TJ, Tobias JH (1993) The estrogen antagonist ICI 182,780 reduces cancellous bone volume in female rats. Endocrinology 133 2787-2791... 

Eriksen EF, Hodgson SF, Eastell R, Cedel SL, O Fallon WM, Riggs BL (1990) Cancellous bone remodeling in type I (postmenopausal) osteoporosis quantitative assessment of rates of formation, resorption, and bone loss at tissue and cellular levels. J Bone Miner Res 5 311-319... 

Hodgskinson R, Currey JD (1993) Separate effects of osteoporosis and density on the strength and stiffness of human cancellous bone. Clin Biomech 8 262-268... 

Ke HZ, Chen HK, Qi H, Pirie CM, Simmons HA, Ma YF, et al. (1995a) Effects of droloxifene on prevention of cancellous bone loss and bone turnover in the axial skeleton of aged, ovariectomized rats. Bone 17 491-496... 

Wright CD, Garrahan NJ, Stanton M, et al. (1994) Effect of long term Tamoxifen therapy on cancellous bone remodeling and structure in women with breast cancer. J Bone Miner Res 9 153-159... 

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. 

The preparation of human bone-derived cells for such a study is a major undertaking in itself. The details are somewhat technical but very important (Beresford etal. 1983a,b) the cells are described as bone-derived because they are a heterogeneous population that includes osteoblasts. During orthopaedic surgery, pieces of cancellous bone, the spongy part, are obtained sterile so that they are free from micro-organisms. The pieces are washed three times... 

Miyakoshi N. Effects of parathyroid hormone on cancellous bone mass and structure in osteoporosis. Curr Pharm Des. 2004 10 2615-2627. 

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