Biomechanical properties of the proximal femur determined in vitro by single-energy quantitative computed tomography

To assess the use of quantitative computed tomography as an in vivo predictor of fracture in the osteoporotic hip, we examined the in vitro relationship between single-energy quantitative computed tomography data, calibrated for scanner drift, and the mechanical properties of trabecular bone from the proximal femur. For 49 samples, the apparent density and ultimate strength were measured and their functional relationship to the computed tomography data determined. Apparent density demonstrated a moderate linear correlation to the computed tomography numbers (R2 = 0.60), and the ultimate strength was related through a power law (R2 = 0.83). In addition, for 8 intact femora, average computed tomographic data from the sub-capital region were moderately correlated to the ultimate fracture load applied under controlled in vitro conditions (R2 = 0.64). The average fracture energy for these femora was 43 J, a value more than an order of magnitude less than the energy available in a fall from standing height, suggesting that fall mechanics are a more important determinant of fracture risk than has been previously thought. The relationship between the energy absorbed to failure and the computed tomography data was best described by a power law (R2 = 0.90). Based on these results, it appears that quantitative computed tomography provides a potentially useful approach for the direct estimate of that component of fracture risk that can be attributed to a reduction in bone strength.