Abstract
Previous studies have shown that microdamage accumulates in bone as a result of physiological loading and occurs naturally in human trabecular bone. The purpose of this study was to determine the factors associated with pre-existing microdamage in human vertebral trabecular bone, namely age, architecture, hardness, mineral and organic matrix. Trabecular bone cores were collected from human L2 vertebrae (n = 53) from donors 54–95 years of age (22 men and 30 women, 1 unknown) and previous cited parameters were evaluated. Collagen cross-link content (PYD, DPD, PEN and % of collagen) was measured on surrounding trabecular bone. We found that determinants of microdamage were mostly the age of donors, architecture, mineral characteristics and mature enzymatic cross-links. Moreover, linear microcracks were mostly associated with the bone matrix characteristics whereas diffuse damage was associated with architecture. We conclude that linear and diffuse types of microdamage seemed to have different determinants, with age being critical for both types.
Highlights
Microcracks are observed within the interstitial bone or in interstitial bone intersecting with osteonal cement lines, and are arrested by osteons. [12,16,17] In cortical bone, microdamage appears to initiate within highly mineralized regions in cortical bone, [18] which is consistent with the linear elastic fracture mechanics theory [19,20]
The end plate of each vertebra was removed, as previously described. [10,35] Trabecular bone volume (BV/TV, %), trabecular thickness (Tb.Th, mm), trabecular number (Tb.N, 1/mm), trabecular separation (Tb.Sp, mm), connectivity density (Conn.D, 1/mm3), degree of anisotropy (DA), and structure model index (SMI), which reflects the rod- versus plate-like nature of the structure, of the excised cores were assessed by microcomputed tomography, using an isotropic voxel size of 20 microns, energy (70 kVp), current (177 mA), integration time (200 ms) and a threshold corresponding to a mineral density around 0.35 g.cm3
Microdamage, Tb.Sp, SMI, the ratio PYD/DPD and crystallinity index increased with age, whereas carbonation, BV/ TV, Tb.N and DA decreased with age (Table 2)
Summary
Nucleation of mineral occurs in the ‘hole’ regions of the collagen arrays and apatite crystals develop in length along the collagen long axes and in width along channels within the collagen sheets In such a two-phase structure, a microcrack would most likely be a break or fissure in the mineral matrix, and in organic matrix. The primary aims of the present study were to determine whether the degree and heterogeneity of mineralization, the mineral and organic characteristics, the microhardness and the collagen cross-links are related to the amount and type of preexisting microdamage (ie: no damage created for this study) independently of age and trabecular bone volume in human vertebral trabecular bone from older donors
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