Strength indices from pQCT imaging predict up to 85% of variance in bone failure properties at tibial epiphysis and diaphysis.

Our primary objective was to validate the Bone Strength Index for compression (BSIC) by determining the amount of variance in failure load and stiffness that was explained by BSIC and bone properties at two distal sites in human cadaveric tibiae when tested in axial compression. Our secondary objective was to assess the variance in failure moment and flexural rigidity that was explained by bone properties, geometry and strength indices in the tibial diaphysis when tested in 4-point bending. Twenty cadaver tibiae pairs from 5 female and 5 male donors (mean age 74 yrs, SD 6 yrs) were measured at the distal epiphysis (4 and 10% sites of the tibial length from the distal end) and diaphysis (50 and 66% sites) by peripheral Quantitative Computed Tomography (pQCT; XCT 2000, Stratec). After imaging, we conducted axial compression tests on the distal tibia and 4-point bending tests on the diaphysis. Total bone mineral content and BSIC (product of total area and squared density of the cross-section) at the 4% site predicted 75% and 85% of the variance in the failure load and 52% and 57% in stiffness, respectively. At the diaphyseal sites 80% or more of the variance in failure moment and/or flexural rigidity was predicted by total and cortical area and content, geometry and strength indices corresponding to the axes of bending.