Mechanical testing and biomechanical CT analysis to assess vertebral flexion strength of Chinese cadavers

Biomechanical CT (BCT), i.e., quantitative computed tomography-based finite element analysis (QCT-FEA), promises an improved technique over bone mineral density (BMD) in predicting bone strength and the risk of osteoporotic vertebral fractures. However, most of the BCT models only consider a uniform compressive loading condition and they have not been validated for Chinese subjects. This study examined the ability of BCT to predict wedge fracture-related vertebral flexion strength in a cohort of Chinese cadaveric vertebrae. Twelve human vertebrae were scanned with dual energy X-ray absorptiometry (DXA) and QCT to measure areal and volumetric BMD, respectively. To produce wedge fractures, the cadaveric vertebrae were experimentally loaded until failure under a 15^° flexion. Vertebral flexion stiffness and strength were measured from the force-displacement curve. Voxel-based heterogeneous FE models of the vertebrae were created and virtually tested in uniform compression and 15^° flexion to compute compressive and flexion strength (and stiffness), respectively. The predictions of vertebral flexion strength with BMD or BCT measures were evaluated with linear regression analyses. Results showed weak correlations between experimentally-measured flexion strength vs. DXA-aBMD (R² = 0.26) or QCT-vBMD (R² = 0.39). However, there were strong correlations between experimentally-measured flexion strength vs. BCT-computed vertebral strength under either flexion (R² = 0.71) or compression (R² = 0.70) loading conditions, although flexion reduced the BCT-computed vertebral strength by 9.2%. These results suggest that, regardless of whether a uniform compression or a flexion loading is simulated, BCT can predict in vitro vertebral flexion strength better than BMD.