CHANGES IN THE FRACTURE-TOUGHNESS OF BONE MAY NOT BE REFLECTED IN ITSMINERAL DENSITY, POROSITY, AND TENSILE PROPERTIES

Age-related changes in the skeleton often lead to an increase in the s usceptibility of bone to fracture. Such changes most likely occur in t he constituents of bone, namely, the mineral and organic phases, and i n their spatial arrangement manifested as orientation and microstructu re. In the past, however, bone loss or decline in bone mineral density has been considered to be the major contributing factor for the incre ased risk of bone fractures, and elastic modulus and ultimate strength have been commonly used to assess bone quality and strength. However, whether these properties provide sufficient information regarding the likelihood of bone to fracture remains debatable. Using a novel fract ure toughness test, which measures the energy or stress intensity requ ired to propagate a crack within a material, the objective of this stu dy was to investigate if the mineral density and mechanical properties of bone can accurately predict bone fragility as measured by fracture toughness. Changes in fracture toughness (K-IC), bone mineral density (BMD), elastic modulus (E), yield and ultimate strength (sigma(y) and sigma(s)), porosity (P-o), and microhardness (H-v) of bone were exami ned as a function of age in a baboon model. With increasing age, the f racture toughness of bone decreased, and its microhardness increased. However, no significant changes were found in BMD, E, P-o, sigma(y), a nd sigma(s) as a function of age. In addition, simple regression analy ses revealed no significant correlation between bone fracture toughnes s and the other parameters, except for microhardness of bone. The resu lts of this study indicate that changes in bone fracture toughness may not be necessarily reflected in its mineral density, porosity, elasti c modulus, yield strength, and ultimate strength. (Bone 23: 67-72; 199 8) (C) 1998 by Elsevier Science Inc. All rights reserved.