A Cortical Thickness Mapping Method for the Coxal Bone Using Morphing

Abstract

As human body finite element models become more integrated with the design of safety countermeasures and regulations, novel models need to be developed that reflect the variation in the population's anthropometry. However, these new models may be missing information which will need to be translated from existing models. During the development of a 5th percentile female occupant model (F05), cortical thickness information of the coxal bone was unavailable due to resolution limits in the computed tomography (CT) scans. In this study, a method for transferring cortical thickness information from a source to a target model with entirely different geometry and architecture is presented. The source and target models were the Global Human Body Models Consortium (GHBMC) 50th percentile male (M50) and F05 coxal bones, respectively. To project the coxal bone cortical thickness from the M50 to the F05, the M50 model was first morphed using a Kriging method with 132 optimized control points to the F05 anthropometry. This technique was found to be accurate with a mean nodal discrepancy of 1.27 mm between the F05 and morphed M50 (mM50) coxal bones. Cortical thickness at each F05 node was determined by taking the average cortical thickness of every mM50 node, non-linearly weighted by its distance to the F05 nodes. The non-linear weighting coefficient, β, had a large effect on the accuracy and smoothness of the projected cortical bone thickness. The optimal projection had β = 4 and was defined when the tradeoff between projection accuracy and smoothness was equal. Finally, a quasi-static pelvis compression was simulated to examine to effect of β. As β, increased from 0 to 4, the failure force decreased by ~100 N, whereas the failure displacement increased by 0.9 mm. Results from quasi-static compression tests of the F05 pelvis were comparable to experimental results. This method could be applied to other anatomical regions where cortical thickness variation is important, such as the femur and ribs and is not limited to GHBMC-family models. Furthermore, this process will aid the development of subject-specific finite element models where accurate cortical bone thickness measurements cannot be obtained.

Effect of Impact Velocity, Flooring Material, and Trochanteric Soft-Tissue Quality on Acetabular Fracture during a Sideways Fall: A Parametric Finite Element Approach

“…The acetabular cortical bone thickness measurement is presented in four cross-sections. The measured thicknesses were consistent with Giudice et al [40], who reported the ranges of 0-2.4 mm and 1.8-3.6 mm for the cortical thicknesses of the acetabular fossa and rim of the acetabulum, respectively. Table A4.…”

“…The location-dependent cortical thickness was obtained via a semi-automated slice-by-slice local thresholding procedure available in Mimics ® . The cortical thicknesses obtained, especially at the acetabulum (the thinnest cortical bone within the pelvis), were checked to make sure that they were in the typical reported range for the pelvic cortical bone [39,40] (Appendix A, Figure A1). Since an abdominal CT image was used in this study, only the proximal part of the femur was reconstructed directly.…”

“…The location-dependent cortical thickness was obtained via slice-by-slice local thresholding (662-1988 HU). The thicknesses obtained were in the typical range [39,40]. The acetabular cortical bone thickness measurement is presented in four cross-sections.…”