Mechanical Properties of Cortical Bone

The mechanical properties of cortical bone (specifically, the femur, tibia, humerus, and radius) of various species (specifically, horse, cattle, pig, and human) in tension, compression, and torsion are listed in Table I. It should be noted, for example, that human femur tensile strength (namely, 124 MPa) (Yamada, 1970) is in the same order of magnitude to that of cast iron (170 MPa) (Beer and Johnston, 1981) but, surprisingly, low in weight (Kaplan et al., 1994 Fung, 1993). These unique properties of bone are a direct consequence of the synergy of its molecular, cellular, and tissue arrangement. 

Mechanical Properties of Cortical Bone in Tension, Compression, and Torsion"... 

Aging also affects the mechanical properties of cortical bone. Tensile ultimate stress decreases at a rate of approximately 2 percent per decade (Fig. 8.7a). Perhaps most important, tensile ultimate strain decreases by about 10 percent of its young value per decade, from a high of almost 5 percent... 

Cowin, S. C. (1989), Mechanical properties of cortical bone, in S. C. Cowin (ed.). Structure and Function of Cortical Bone, pp. 97-127, CRC Press, Boca Raton, Fla. 

Currey, J.D. (1988) The effects of drying and re-wetting on some mechanical properties of cortical bone. J. Biomech., 21, 439-441. 

Reilly, D.T. and Burstein, A.H. (1974) The mechanical properties of cortical bone. J. Bone Joint Surg., 56A, 1001-1022... 

Wang T, Feng Z. Dynamic mechanical properties of cortical bone the effect of mineral content. Mater Lett 2005 59(18) 2277-80. 

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. 

Keaveny, T. M., and Hayes, W. C., Mechanical properties of cortical and trabecular bone. Bone 1,285-344 (1993). 

In the early stages of bone formation, the osteons dominate the bone structure to make an overall structure of fiber-matrix composite. While the primary bone has a dense structure, the secondary bone structure is this composite. As a result, the cortical bone structure becomes very complex. It is microscopically porous, has a lamellar structure, and is also a fiber-matrix composite. Size and packing of osteons and canals, and their orientation, determine the mechanical properties of these bones. 

Table 16.1 Mechanical properties of cortical and trabecular bone...

All bones consist of a basic dual structure an external layer, named cortical bone, which covers the bone it is smooth, continuous and dense (approximately 1.85 g/cm ). In the interior, cancellous bone is porous (with an open, honeycomb structure) with an average porosity of 75% to 95% and an average density of 0.3 g/ cm [4]. The main physical and mechanical properties of cortical and cancellous bone are snmmarized in Table 15.2 [1-6]. As described below, the cortical bone has an anisotropic strnctnre [7] and hence anisotropic mechanical properties for this reason, Table 15.2 collects valnes determined nnder both longitudinal and transverse directions of the applied load. 

Mechanical and Degradation Properties. Studies characterizing the mechanical properties of these highly crosslinked materials indicate properties that are intermediate between those of cortical and trabecular bone. Table I summarizes these results along with the mechanical properties of bone. 

T.A. Einhorn, G.K. Wakley, S. Linkhart, E.B. Rush, S. Maloney, E. Faierman, D. J. Baylink, Incorporation of sodium fluoride into cortical bone does not impair the mechanical properties of the appendicular skeleton in rats, Calcif. Tissue Int. 51 (1992) 127-131. 

Table 5.15 Comparison of Some Mechanical Properties of Current Implant Materials with Those of Cortical Bone...

Typically, bone has a solid outer portion called cortical bone and a porous inner part called cancellous bone. The amounts of each vary with location in the body. The cortical bone is a ceramic containing calcium compounds and viscous liquids, a protein called collagen , and an organic polymer. In addition to HAP, bone consists of calcium carbonate and calcium phosphate. HAP is 69 wt.% of total calcium phosphate compounds [4]. Part of the Ca in these compounds is substituted by Na, K, Mg, and Sr. Hydroxyl ions in the HAP are also substituted by F, CO3, or Cl, which makes the apatite a fluoroapatite, dahllite or chloroapatite, respectively. These substitutions are considered to play significant roles in the structure and mechanical properties of bones. 

Cancellous bone is a very porous material, with an average density of 1.3gcm, implying a porosity of nearly 35%. In practice, the density lies between 5 and 95% varying gradually between cortical and cancellous regions. The pore size distribution is bimodal. The pores are elongated and filled with soft tissues that include bone marrow, blood vessels, and various bone-related cells. It is the overall porosity and the pore size distribution that mostly control the mechanical properties of bone. 

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