Bone Elasticity and Ultrasound Velocity Are Affected by Subtle Changes in the Organic Matrix

Abstract

The mechanical competence of bone can be studied through the measurement of the components of its material elasticity, a property which can vary both in magnitude and in dependence upon orientation (anisotropy). While it is known that the elasticity is largely determined by the mineral constituents of the bone matrix, it is nonetheless clear that it must be also dependent upon the remaining constituents of bone material. In this work, the influence of organic components on the elasticity is explored by altering specific constituents of the bone matrix to varying degrees. This study addresses two questions: first, are the resulting changes in elasticity strongly or weakly dependent upon direction, and second, are they substantially dependent upon the nature and magnitude of the induced matrix alteration? To answer these questions, we performed different chemical manipulations of the bone matrix and measured the changes in elasticity and velocity using the technique of ultrasound critical angle reflectometry. Altering the properties of the organic matrix resulted in substantial and complex changes in the elasticity of bone. The observed changes were strongly dependent upon direction, could not be explained by changes in density alone, and varied strongly with the specific chemical treatment of the matrix. Immersion in urea selectively affected protein components of the organic matrix and resulted in reversible changes in velocity and elasticity, while removal of collagen caused anisotropic decreases and removal of all organic matter caused a collapse of all components of the elasticity. In conclusion, this study confirms that the organic matrix exerts a profound influence on the elasticity and indicates that the measurement of elastic properties at multiple directions is necessary in the assessment of bone mechanical competence. (J Bone Miner Res 1998;13:114-121)

Effect of Collagen and Mineral Content on the High-Frequency Ultrasonic Properties of Human Cancellous Bone

“…In contrast, the anisotropy of SOS was preserved after decollagenization, indicating that the anisotropy in SOS is independent of collagen content. This result is consistent with experiments from other laboratories on cortical bone [5,6]. It is interesting to note that ultrasonic measurements performed on bovine Achilles tendon have shown that oriented collagen fibers can produce a large anisotropy in SOS [16].…”

“…Both types of measurements correlate well with bone mineral density (BMD), and are sensitive to the anisotropic microstructure of bone. These measurements also may be sensitive to the protein matrix of bone [4][5][6][7]. Recent work by a few investigators has drawn attention to the possibility of developing new techniques based on ultrasonic backscatter [8][9][10][11].…”

Apparent viscoelastic anisotropy as measured from nondestructive oscillatory tests can reflect the presence of a flaw in cortical bone

“…Techniques based on vibrational or wave propagation principles that have in vivo applications have been successful in detecting age-and disease-related changes in bone properties, 37,38 the effect of large structural defects on whole bone properties, 39,40 and in predicting the effect of microstructure, 41 bone mineral, 42 and organic components 43 on bone-tissue properties. The effect of mechanical damage on bone-tissue properties, however, has proven difficult to predict using similar means 44 despite their usefulness in detecting damage in engineering materials.…”

Quantitative Ultrasound Methods to Assess Bone Mineral Status in Children: Technical Characteristics, Performance, and Clinical Application

“…It should be considered that QUS parameters are influenced not only by bone density as occurs for DXA, but also by bone structure and composition, so that they give additional information, compared with DXA, on some aspect regarding bone quality (7,8,10). In fact, some QUS parameters are able to detect collagen and organic matrix abnormalities in vitro (76,78) and in vivo (79), giving some information on the organic components of bone material. Anyway, there are too few data linking bone mineral status by DXA, pQCT, or QUS measure to fracture rate in children, and further studies in a large number of subjects are needed to investigate this crucial aspect.…”