Measurements of mobile and bound water by nuclear magnetic resonance correlate with mechanical properties of bone

Abstract

Since clinical measures of bone mineral density do not necessarily predict whether a person will fracture a bone without an intervention, there is a need to find supplementary tools for assessing bone quality. Presently, we hypothesized that measures of mobile and bound water by a Nuclear Magnetic Resonance (NMR) technique are correlated with bone strength and toughness, respectively. To test this, bending specimens from the mid-diaphysis of 18 human femurs were collected from 18 male donors and divided into middle aged and elderly groups. After NMR measurements of each hydrated specimen, an inversion technique was used to convert the free induction decay data into a distribution of spin-spin (T2) relaxation rates. Then, the distribution resolved into three distinct components that likely represent solid hydrogen, water bound to bone tissue, and mobile water that occupy microscopic pores within the bone specimen. The integrated signal intensities of the bound and mobile components were normalized by the wet mass of the specimen. Following NMR measurements, three point bending tests were conducted to determine the modulus of elasticity, flexure strength, and work to fracture of each specimen. Next, the porosity, mineral-to-collagen ratio, and pentosidine concentration were measured. In this sample of human cortical bone, there was no age-related difference in the amount of mobile water, but the decrease in the amount of bound water with increasing age was statistically significant. Moreover, bound water was associated with both strength and work to fracture of bone, while mobile water was correlated with modulus of elasticity and appeared to quantify the level of microscopic pores within bone. On the other hand, bound water was correlated with the concentration of non-enzymatic collagen crosslinks. The results of this study indicate that quantifying mobile and bound water with magnetic resonance techniques could potentially serve as indicators of bone quality.

In Vivo Quantitative MR Imaging of Bound and Pore Water in Cortical Bone

“…(Although one of these previous studies [32] included soft-tissue signal suppression, which likely suppressed some portion of the pore water signal.) of bone (19,20). Low bound water measurements could account for the disproportionate increase in fracture risk compared with the decrease in bone density measurements in type 2 diabetes or in aging populations that have demonstrated increased brittleness that cannot be measured with current x-ray methods (27,28).…”

“…These methods have no ionizing radiation and allow for new quantitative measurements that are known to reflect the material properties of bone (18)(19)(20).…”

“…Eligible volunteers included 20-80-year-old healthy adults. Exclusion criteria included volunteers with non-MR imaging compatible implants or cerebral aneurysm clips; volunteers who may have had shrapnel embedded in their bodies; volunteers younger than 20 years of age; pregnant women; and volunteers including yield stress, peak stress, and elastic toughness (18)(19)(20). Bone specimens with a greater concentration of bound water tend to have high peak and yield stress values and elastic toughness, whereas specimens with a greater concentration of pore water are generally associated with higher porosity and lower peak stress, yield stress, and toughness.…”

Assessment of femoral bone osteoporosis in rats treated with simvastatin or fenofibrate

“…The 1 H CPMG (CarrPurcell-Meiboom-Gill) pulse sequence is a NMR method which correlated with Laplace inversion analysis lead to a relaxation T 2 spectrum that can be used to determine the porosity and to assess the pore size distribution in bone [10]. There are just a few studies by NMR spectroscopy [11] or relaxometry [12] on rats' bones or rat optical nerve and frog sciatic nerve [13], but there are many studies of human cortical bone by 1 H NMR relaxometry in particular 1D T 2 distribution [14][15][16][17][18][19] or 2D T 2 -T 2 exchange maps [20,21].…”

Measurement of the Mechanical Properties of Bone: A Recent History

“…NMR spectroscopy measures the amount of water in different compartments in the bone, bound and mobile particularly. For example, Nyman et al [36] found that in men's bones the amount of bound water decreased with age, and the toughness decreased concomitantly. Synchrotron radiation can be used in various modes, either as a source of light to examine strains in the different components of bone [22] or for more straightforward tomography, producing images of relatively large specimens [52].…”