Development of Quantitative Computed-Tomography-Based Strength Indicators for the Identification of Low Bone-Strength Individuals in a Clinical Environment

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The aim of this study was to develop quantitative computed-tomography (QCT)-based bone-strength indicators that highly correlate with finite-element (FE)-based strength. Transaxial QCT scans were obtained from 36 major, cadaveric, long bones (humerus, radius, femur and tibia) from 4 females and 2 males, 53 to 86 years old. These images were used to construct the FE models and to develop the QCT-based bone strength indicators under every-day, simplified loading conditions.

We have evaluated the performance of area-weighted (AW), density-weighted (DW) and modulus-weighted (MW) rigidity measures as well as popular strength indicators like section modulus (Z) and stress–strain index (SSI). We have also developed a novel strength metric, the centroid deviation, which analyzes the spatial distribution of the centroids along the length of the bone. The correlation results show that the MW polar moment of inertia and the MW moment of inertia are the two top-performers for all bones and loading conditions (average r > 0.89). The MW centroid deviations correlated highly with the estimated load to fracture for all bones under compression (r > 0.83), except for the humerus (r = 0.67). Consistently DW or MW rigidity measures produced a statistically significant improvement in capturing bone strength compared to AW rigidity measures. As expected, MW rigidity measures showed a higher correlation with the FE-based fracture load than the DW rigidity measures; however, the improvement was not statistically significant.

Through this study we present a short-list of useful QCT-based strength parameters that correlate well with FE-based fracture load. Although a few parameters perform reasonably well across most bones and loading conditions, a judicious assessment of bone strength should include multiple parameters evaluated at multiple critical locations in the long bones, with attention to the type of loading and bone type.