Trabecular bone strength

Picherit et al., 2000 1 yr old OVX rats oral administration, 90 d genistein or daidzein at 10 mg/kg body weight Overall daidzein > genistein in this study. Total femoral BMD losses and vertebral trabecular bone were protected by estradiol and daidzein, but genistein was not efficient. Bone strength (femoral failure stress) protected by estradiol, daidzein and genistein... 

The human skeleton consists of both cortical and trabecular bone. Cortical bone is dense and compact and is responsible for much of bone strength. It is the most common type of... 

FIGURE 8.11 Dependence of ultiinaie stress on age for trabecular bone from the human vertebra and femur. For both anatomic sites, strength decreases approximately 10 percent per decade. (Data from Rrfs. 15 and 149.)... 

Interestingly, the failure (yield and ultimate) strains of human trabecular bone have only a weak dependence, if any, on apparent density and modulus." - - - A recent study designed to test for intersite differences found that yield strains were approximately uniform within anatomic sites, with standard deviations on the order of one-tenth the mean value, but mean values could vary across sites" (Fig. 8.13). Thus, for analysis purposes, yield strains can be considered constant wiAin sites but heterogeneous across sites. Regardless of anatomic site, however, yield stains are higher in compression than in tension." Ultimate strains are typically in the range of 1.0 to 2.5 percent. Evidence from experiment on bovine bone indicates that yield strains are also isotropic - despite substantial anisotropy of modulus and strength. 

Criteria such as the Tsai-Wu criterion have only a limited ability to describe multiaxial failure of trabecular bone for arbitrary stress states. Coupling between normal strengths in different directions (longitudinal versus transverse, for example) appears to be minimal. 

Keaveny, T. M., Wachtel, E. F., Ford, C. M., and Hayes, W. C. (1994), Differences between the tensile and compressive strengths of bovine tibial trabecular bone dqioid on modulus,/. Biomech. 27 1137-1146. 

Niebur, G. L., Feldstein, M. J., Yuen, J. C., Chen, T. J., and Keaveny, T. M. (2000), High-resolution finite element models with tissue strength asymmetry accurately predict failure of trabecular bone, J. Biomech. 33 1575-1583. 

Mosekilde, L., and Mosekilde, L. (1986), Normal vertebral body size and compressive strength Relations to age and to vertebral and iliac trabecular bone compressive strength. Bone 7 207-212. 

The relationships between the static mechanical properties of trabecular bone and apparent density vary for the different types of trabecular bone because of the anatomic site-, age-, and disease-related variations in trabecular architecture. Both linear and power-law relationships can be used to describe the dependence of modulus and compressive strength on apparent density (Tables A2.2, A2.3), with typical coefficients of determination (r values) in the range 0.5-0.9. Differences in the predictive... 

Table A2.1 Typical wet apparent densities, moduli, and compressive strengths for human trabecular bone... 

Yaszemski, M.J., Mikos, A.G., Payne, R.G. and Hayes, W.C. (1994) Biodegradable Polymer Composites for Temporary Replacement of Trabecular Bone The Effect of Polymer Molecular Weight on Composite Strength and Modulus, In Biomatetials for Drug and Cell Delivery, Mikos. A.G., Murphy R., Bernstein H., Peppas N..V., eds., 331, Pittsburgh Materials Research Society) 251-256. 

Because of the trabecular structure of bones, they can withstand stress through pressure or tensile force. The strength of bone substance lies between 110 to 170 N/mm and the elasticity module ranges from 19,000... 

Due to the inferior biomechanical properties, Ca-P ceramics are less suitable for cHnical appHcation under weight-bearing conditions compared to, for example, metallic or polymeric biomaterials. Obviously, mechanical properties of porous ceramics deteriorate even further with an increasing porosity. Nevertheless, compressive strengths similar to trabecular bone have been reported [7],... 

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