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Evaluation of Changes in Trabecular Bone Architecture and Mechanical Properties of Minipig Vertebrae by Three‐Dimensional Magnetic Resonance Microimaging and Finite Element Modeling
Author(s) -
Borah B.,
Dufresne T. E.,
Cockman M. D.,
Gross G. J.,
Sod E. W.,
Myers W. R.,
Combs K. S.,
Higgins R. E.,
Pierce S. A.,
Stevens M. L.
Publication year - 2000
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1359/jbmr.2000.15.9.1786
Subject(s) - anatomy , vertebra , trabecular bone , magnetic resonance imaging , materials science , volume (thermodynamics) , biomedical engineering , trabecula (gastropod) , osteoporosis , biology , medicine , pathology , radiology , physics , botany , quantum mechanics , genus
Abstract The study objective was to analyze the three‐dimensional (3D) trabecular architecture and mechanical properties in vertebral specimens of young and mature Sinclair minipigs to assess the relative contribution of architecture to bone strength. We used 3D magnetic resonance microimaging (MRμI) and direct image analysis to evaluate a set of standard structural measurements and new architectural descriptors of trabecular bone in biopsy specimens from L2, L3, and L4 vertebrae ( n = 16 in each group) from young (mean age, 1.2 years) and mature (mean age, 4.8 years) minipigs. The measurements included bone volume/tissue volume (BV/TV), marrow star volume (Ma.St.V), connectivity density (ConnD), and two new parameters, percent platelike trabeculae (% plate) and percent bone in the load direction (% bone LD ). The % plate, calculated from surface curvature, allowed the delineation of plates from rods. The % bone LD quantified the percentage of bone oriented along the long axis of the vertebral body. We showed that 3D MRμI can detect the subtle changes in trabecular architecture between the two age groups. ConnD, star volume, % plate, % bone LD , and BV/TV were found to be more effective than the model‐based, derived indices (trabecular thickness [Tb.Th], trabecular separation [Tb.Sp], and trabecular number [Tb.N]) in differentiating the structural changes. BV/TV, % plate, and % bone LD significantly increased ( p < 0.05) in all three vertebral sites of the mature minipigs. The significant decrease in ConnD and star volume in the mature vertebra was consistent with the concurrent increase of platelike trabecular bone ( p < 0.05). Overall, ConnD, star volume, % plate, and % bone LD provided a coherent picture of the architectural changes between the two age groups. Apparent modulus and maximum stress were determined experimentally on biopsy specimens from L2 vertebrae ( n = 16). When apparent modulus was predicted using 3D MRμI data sets as input for finite element modeling (FEM), the results were similar to the experimentally determined apparent modulus ( p = 0.12). Both methods were then used to compare the young and the mature animals; the experimental and predicted apparent modulus were significantly higher for the mature group ( p = 0.003 and 0.012, respectively). The experimental maximum stress in the vertebra of the mature animals was twice as high as that for the young animals ( p = 0.006). Bone quantity (BV/TV or bone mineral content [BMC]) alone could explain approximately 74–85% of the total variability in stress and modulus. The inclusion of either ConnD or % bone LD with BV/TV in a multiple regression analysis significantly improved the predictability of maximum stress, indicating that architecture makes additional contributions to compressive strength in normal minipig vertebra.