Increased calcium content and inhomogeneity of mineralization render bone toughness in osteoporosis: mineralization, morphology and biomechanics of human single trabeculae

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Busse, Björn^1,2; Hahn, Michael¹; Soltau, Markus¹; Zustin, Jozef³; Püschel, Klaus⁴; Duda, Georg N.²; Amling, Michael¹

Increased calcium content and inhomogeneity of mineralization render bone toughness in osteoporosis: mineralization, morphology and biomechanics of human single trabeculae

Bone. December 2009;45(6):1034-1043

©2009 Elsevier Inc. All rights reserved

Affiliations

¹Center for Biomechanics and Skeletal Biology, University Medical Center Hamburg‐Eppendorf, Lottestr. 59, D-22529 Hamburg, Germany

²Julius Wolff Institute and Center for Musculoskeletal Surgery, Charité-University Medicine Berlin, Augustenburger Platz 1, D-13353 Berlin, Germany

³Institute of Pathology, University Medical Center Hamburg‐Eppendorf, Martinistraβe 52, D-20246 Hamburg, Germany

⁴Institute of Legal Medicine, University Medical Center Hamburg‐Eppendorf, Martinistraβe 52, D-20246 Hamburg, Germany
Abstract and keywords

The differentiation and degree of the effects of mineral content and/or morphology on bone quality remain, to a large extent, unanswered due to several microarchitectural particularities in spatial measuring fields (e.g., force transfer, trajectories, microcalli). Therefore, as the smallest basic component of cancellous bone, we focused on single trabeculae to investigate the effects of mineralization and structure, both independently and in superposition. Transiliac Bordier bone cores and T12 vertebrae were obtained from 20 females at autopsy for specimen preparation, enabling radiographical analyses, histomorphometry, Bone Mineral Density Distribution (BMDD) analyses, and trabecular singularization to be performed. Evaluated contact X-rays and histomorphometric limits from cases with osteoporotic vertebral fractures generated two subdivisions, osteoporotic (n = 12, Ø 78 years) and non-osteoporotic (n = 8, Ø 49 years) cases, based on fracture appearance and bone volume (BV/TV). Measurements of trabecular number (Tb.N.), trabecular separation (Tb.Sp.), trabecular thickness (Tb.Th.), trabecular bone pattern factor (TBPf) and eroded surface (ES/BS) were carried out to provide detailed structural properties of the investigated groups. The mechanical properties of 400 rod-like single vertebral trabeculae, assessed by three-point bending, were matched with mineral properties as quantified by BMDD analyses of cross-sectioned rod-like and plate-like trabeculae, both in superposition and independently. Non-osteoporotic iliac crests and vertebrae displayed linear dependency on structure parameters, whereas osteoporotic compartments proved to be non-correlated with bone structure. Independent of trabecular thickness, osteoporotic rod-like trabeculae showed decreases in Young's modulus, fracture load, yield strength, ultimate stress, work to failure and bending stiffness, along with significantly increased mean calcium content and calcium width. Non-osteoporotic trabeculae showed biomechanically beneficial properties due to a homogeneous mineralization configuration, whereas osteoporotic trabeculae predominantly demonstrated various mineralized bone packets, eroded surfaces, highly mineralized cement lines and microcracks. The Young's moduli of single trabeculae exhibited significantly negative linear correlations with trabecular thickness. Because of increased, but inhomogeneously distributed, calcium content, osteoporotic trabeculae may be subject to shear stresses that render bone fragile beyond structure impairment due to cracks and lacunae.

Keywords: Osteoporosis; Biomechanics; Materials testing; Bone histomorphometry; Bone mineralization
Links

DOI: 10.1016/j.bone.2009.08.002

PubMed: 19679206

WoS: 000271916900001
History

Received: 2009-03-17

Revised: 2009-07-13

Accepted: 2009-08-03

Online: 2009-08-11

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