Bone fragility beyond strength and mineral density: Raman spectroscopy predicts femoral fracture toughness in a murine model of rheumatoid arthritis

Abstract

Clinical prediction of bone fracture risk primarily relies on measures of bone mineral density (BMD). BMD is strongly correlated with bone strength, but strength is independent of fracture toughness, which refers to the bone’s resistance to crack initiation and propagation. In that sense, fracture toughness is more relevant to assessing fragility-related fracture risk, independent of trauma. We hypothesized that bone biochemistry, determined by Raman spectroscopy, predicts bone fracture toughness better than BMD. This hypothesis was tested in tumor necrosis factor-transgenic mice (TNF-tg), which develop inflammatory-erosive arthritis and osteoporosis. The left femurs of TNF-tg and wild type (WT) littermates were measured with Raman spectroscopy and micro-computed tomography. Fracture toughness was assessed by cutting a sharp notch into the anterior surface of the femoral mid-diaphysis and propagating the crack under 3 point bending. Femoral fracture toughness of TNF-tg mice was significantly reduced compared to WT controls (p=0.04). A Raman spectrum-based prediction model of fracture toughness was generated by partial least squares regression (PLSR). Raman spectrum PLSR analysis produced strong predictions of fracture toughness, while BMD was not significantly correlated and produced very weak predictions. Raman spectral components associated with mineralization quality and bone collagen were strongly leveraged in predicting fracture toughness, reiterating the limitations of mineralization density alone.

Overconstrained library-based fitting method reveals age- and disease-related differences in transcutaneous Raman spectra of murine bones

“…Blind decomposition methods, 55,56 if properly constrained, could also potentially be used to estimate bone spectra based on transcutaneous measurements. The results of this study demonstrate that the mineral/matrix ratio of cortical bone, which has frequently been used as a Raman-based indicator of bone health and strength, [4][5][6][7][8][9][10][11][12][13][14] can be measured transcutaneously by processing SORS data sets with SOLD ( Figs. 10 and 11).…”

“…2 Vibrational spectroscopy has been used extensively in ex vivo studies to measure the chemical composition of both the mineral and organic matrix components of bone. 3,4 Specifically, Raman spectroscopy has revealed chemical perturbations to cortical bone in animal studies of aging, 5 lead exposure, 6 osteogenesis imperfecta, 7 early-onset osteoarthritis, 8 rheumatoid arthritis, 9 and glucocorticoid-induced osteoporosis 10,11 and in a study of women with postmenopausal osteoporosis. 12 Many studies have also revealed correlations between Raman spectroscopy-based measures of chemical composition and the biomechanical properties of bone.…”

“…5,13,14 In fact, preliminary studies from our group indicate that Raman spectra can generate predictions of biomechanical strength and toughness that are more accurate than those produced by the clinically used parameter of BMD. 6,9,10 These results on exposed-bone samples have inspired attempts to perform bone spectroscopy transcutaneously. [15][16][17][18][19][20][21][22][23][24] Tissue phantoms with controlled optical and chemical properties have also been developed to model transcutaneous measurements.…”

Polarization in Raman spectroscopy helps explain bone brittleness in genetic mouse models

“…32 Although each would require significant empirical support to extend mechanistically to analysis of turbid bone tissue, unsupervised multivariate analysis allows for the influence of these known RS sensitivities to be related to mechanical outcomes without spurious mechanistic suppositions. Indeed, recent applications of multivariate RS analyses to bone have helped explain the fracture toughness of bone in a model of rheumatoid arthritis 33 as well as partial mechanical improvement of OI mouse bones after human stem cell transplant. 34 Therefore, we investigated the potential of full spectrum multivariate analysis with a "bottom-up" design built upon the principal directions of Raman variance between test groups.…”

Co-localized confocal Raman spectroscopy and optical coherence tomography (CRS-OCT) for depth-resolved analyte detection in tissue

“…For instance, optical coherence tomography (OCT) can measure depth-resolved tissue morphology up to one millimeter below the tissue surface [3,4] depending upon the type of tissue and its associated optical properties. Chemically-sensitive optical methods, such as Raman spectroscopy (RS) [5][6][7][8][9][10][11], can measure spatiotemporal distributions of analytes with up to micron-level spatial resolution when utilizing confocal detection [12]. In fact, confocal Raman spectroscopy has been recently applied, using commercially-available instrumentation, to detect Tenofovir in tissue samples ex vivo [13].…”