Assessing matrix quality by Raman spectroscopy helps predict fracture toughness of human cortical bone

Developing clinical tools that assess bone matrix quality could improve the assessment of a person's fracture risk. To determine whether Raman spectroscopy (RS) has such potential, we acquired Raman spectra from human cortical bone using microscope- and fiber optic probe-based Raman systems and tested whether correlations between RS and fracture toughness properties were statistically significant. Calculated directly from intensities at wavenumbers identified by second derivative analysis, Amide I sub-peak ratio I₁₆₇₀/I₁₆₄₀, not I₁₆₇₀/I₁₆₉₀, was negatively correlated with K_init (N = 58; R² = 32.4%) and J-integral (R² = 47.4%) when assessed by Raman micro-spectroscopy. Area ratios (A₁₆₇₀/A₁₆₉₀) determined from sub-band fitting did not correlate with fracture toughness. There were fewer correlations between RS and fracture toughness when spectra were acquired by probe RS. Nonetheless, the I₁₆₇₀/I₁₆₄₀ sub-peak ratio again negatively correlated with K_init (N = 56; R² = 25.6%) and J-integral (R² = 39.0%). In best-fit general linear models, I₁₆₇₀/I_1640, age, and volumetric bone mineral density explained 50.2% (microscope) and 49.4% (probe) of the variance in K_init. I₁₆₇₀/I₁₆₄₀ and v₁PO₄/Amide I (microscope) or just I₁₆₇₀/I₁₆₄₀ (probe) were negative predictors of J-integral (adjusted-R² = 54.9% or 37.9%, respectively). While Raman-derived matrix properties appear useful to the assessment of fracture resistance of bone, the acquisition strategy to resolve the Amide I band needs to be identified.