Components of micro-architecture and bone density that contribute to biomechanical characteristics of bone. A study in ewe femora.

Abstract

Many components of bone quality contribute to the different aspects of biomechanical competence of bone, including bone mineral density (BMD) and microarchitectural parameters. We analysed the correlation between biomechanical characteristics and measurements of BMD and microarchitecture in the femora of adult ewes. Methods: Twenty-eight middle aged (5-8 years old) ewes were part of a study of the effect of calcitonin on bone after ovariectomy (OVX) (JBMR, 2005:125). The animals were euthanized 6 months post-OVX. The femoral neck BMD was measured by dual x-ray absorptiometry (DXA). Compressive testing was performed on femoral trabecular cylinder corres of 8mm in diameter and 10mm in length with the axis of the cylinder aligned with the axis of the neck. Microarchitecture of femoral neck was examined with a magnetic resonance imager at 9.4 Tesla in axial, coronal and sagital planes at contralateral site. Uni- and multivariate analyses were performed between biomechanics, BMD and MR. Results: In univariate analysis, strenght and stiffness were correlated with DXA and with several components of microarchitecture. Toughness correlated with MR, but not with BMD. In a multivariate stepwise regression analysis, strength and stiffness correlated with BMD and TV/BV, while toughness was related to the mean length of the branches. Conclusions: Biomechanical characteristics show variable correlations wit BMD and microachitecture. These results indicate that microachitecture of trabecular bone contributes significantly to its biomechanical characteristics, independent of BMD measured in the femoral neck.