In Vivo Assessment of Architecture and Micro-Finite Element Analysis Derived Indices of Mechanical Properties of Trabecular Bone in the Radius |
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Authors: | D C Newitt S Majumdar B van Rietbergen G von Ingersleben S T Harris H K Genant C Chesnut P Garnero B MacDonald |
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Institution: | (1) Magnetic Resonance Science Center, University of California, San Francisco, USA, US;(2) University of Eindhoven, Eindhoven, The Netherlands, NL;(3) University of Washington, Seattle, USA, US;(4) Osteoporosis and Arthritis Research Group, University of California, San Francisco, USA, US;(5) INSERM, Unit 403, Lyon, France;, FR;(6) Smith Kline Beecham Pharmaceuticals, USA, US |
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Abstract: | Measurement of microstructural parameters of trabecular bone noninvasively in vivo is possible with high-resolution magnetic
resonance (MR) imaging. These measurements may prove useful in the determination of bone strength and fracture risk, but must
be related to other measures of bone properties. In this study in vivo MR imaging was used to derive trabecular bone structure
measures and combined with micro-finite element analysis (μFE) to determine the effects of trabecular bone microarchitecture
on bone mechanical properties in the distal radius. The subjects were studied in two groups: (I) postmenopausal women with
normal bone mineral density (BMD) (n= 22, mean age 58 ± 7 years) and (II) postmenopausal women with spine or femur BMD −1 SD to −2.5 SD below young normal (n= 37, mean age 62 ± 11 years). MR images of the distal radius were obtained at 1.5 T, and measures such as apparent trabecular
bone volume fraction (App BV/TV), spacing, number and thickness (App TbSp, TbN, TbTh) were derived in regions of interest
extending from the joint line to the radial shaft. The high-resolution images were also used in a micro-finite element model
to derive the directional Young’s moduli (E1, E2 and E3), shear moduli (G12, G23 and G13) and anisotropy ratios such as E1/E3.
BMD at the distal radius, lumbar spine and hip were assessed using dual-energy X-ray absorptiometry (DXA). Bone formation
was assessed by serum osteocalcin and bone resorption by serum type I collagen C-terminal telopeptide breakdown products (serum
CTX) and urinary CTX biochemical markers. The trabecular architecture displayed considerable anisotropy. Measures of BMD such
as the ultradistal radial BMD were lower in the osteopenic group (p<0.01). Biochemical markers between the two groups were comparable in value and showed no significant difference between the
two groups. App BV/TV, TbTh and TbN were higher, and App TbSp lower, in the normal group than the osteopenic group. All three
directional measures of elastic and shear moduli were lower in the osteopenic group compared with the normal group. Anisotropy
of trabecular bone microarchitecture, as measured by the ratios of the mean intercept length (MIL) values (MIL1/MIL3, etc.),
and the anisotropy in elastic modulus (E1/E3, etc.), were greater in the osteopenic group compared with the normal group.
The correlations between the measures of architecture and moduli are higher than those between elastic moduli and BMD. Stepwise
multiple regression analysis showed that while App BV/TV is highly correlated with the mechanical properties, additional structural
measures do contribute to the improved prediction of the mechanical measures. This study demonstrates the feasibility and
potential of using MR imaging with μFE modeling in vivo in the study of osteoporosis.
Received: 13 December 2000 / Accepted: 30 May 2001 |
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Keywords: | :Magnetic resonance imaging – Mechanical properties – Trabecular bone architecture |
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