Journal of Biomechanics 38 (2005) 1229–1237 Interrelationship of trabecular mechanical and microstructural properties in sheep trabecular bone Erik Mittra, Clinton Rubin, Yi-Xian Qin à Department of Biomedical Engineering, Stony Brook University, Psychology-A Building, 3rd Floor, Stony Brook, NY 11794-2580, USA Accepted 28 June 2004 Abstract The ability to evaluate fracture risk at an early time point is essential for improved prognostics as well as enhanced treatment in cases of bone loss such as from osteoporosis. Improving the diagnostic ability is inherent upon both high-resolution non-invasive imaging, and a thorough understanding of how the derived indices of structure and density relate to its true mechanical behavior. Using sheep femoral trabecular bone with a range of strength, the interrelationship of mechanical and microstructural parameters was analyzed using multi-directional mechanical testing and micro-computed tomography. Forty-five cubic trabecular bone samples were harvested from 23 adult female sheep, some of whom had received hind-limb vibratory stimuli over the course of 2 years with consequently enhanced mechanical properties. These samples were pooled into a low, medium, or high strength group for further analysis. The findings show that mCT indices that are structural in nature, e.g., structural model index (SMI) (r 2 ¼ 0:85, po0:0001) is as good as more density oriented indices like bone volume/total volume (BV/TV) (r 2 ¼ 0:81, po0:0001) in predicting the ultimate strength of a region of trabecular bone. Additionally, those indices more related to global changes in trabecular structure such as connectivity density (ConnD) or degree of anisotropy (DA) are less able to predict the mechanical poperties of bone. Interrelationships of trabecular indices such as trabecular number (TbN), thickness (TbTh), and spacing (TbSp) provide clues as to how the trabecular bone will remodel to ultimately achieve differences in the apparent mechanical properties. For instance, the analysis showed that a loss of bone primarily affects the connectedness and overall number of trabeculae, while increased strength results in an increase of the overall thickness of trabeculae while not improving the connectedness. Certainly, the mCT indices studied are able to predict the bulk mechanical properties of a trabecular ROI well, leaving unaccounted only about 15–20% of its inherent variability. Diagnostically, this implies that future work on the early prediction of fractureriskshouldcontinuetoexploretheroleofbonequalityasthekeyfactorsorasanadjuvanttobonequantity(e.g.,apparent density). r 2004 Elsevier Ltd. All rights reserved. Keywords: Micro-CT; Bone microstructure; Bone density; Bone strength; Osteoporosis; Bone remodeling 1. Introduction The ability to accurately assess bone quality in vivo is essential for improving the diagnostic and therapeutic goals for bone loss from such varied etiologies as osteoporosis, microgravity, bed rest, or stress-shielding from an implant. Early diagnostic ability is important because the effectiveness of treatment diminishes with disease progression, yet patients are rarely symptomatic before considerable bone loss has occurred—and some- times not until after the first fracture (Davidson, 2003; Homminga et al., 2004). Traditionally, the focus of clinical bone evaluation has been apparent bone mineral density (BMD) as measured by dual energy X-ray absorptiometry or DEXA (Kanis et al., 2002; Brunader and Shelton, ARTICLE IN PRESS www.elsevier.com/locate/jbiomech www.JBiomech.com 0021-9290/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jbiomech.2004.06.007 à Corresponding author. Tel.: +1-631-632-1481; fax: +1-631-632- 8577. E-mail address: yi-xian.qin@sunysb.edu (Y.-X. Qin).