title: The Effect of Rib Shape on Stiffness.
abstract: This study investigates the isolated effect of rib shape on the mechanical characteristics of ribs subjected to multiple forms of loading. It aims to measure the variation in stiffness due to shape that is seen throughout the population and, in particular, provide a tool for researchers to better understand the influence of shape on resulting stiffness. A previously published six-parameter shape model of the central axis of human ribs was used. It has been shown to accurately model the overall rib path using intrinsic geometric properties such as size, aspect ratio, and skewness, through shapes based on logarithmic spirals with high curvature continuity. In this study the model was fitted to 19,500 ribs from 989 adult female and male CT scans having demographic distributions matching the US adult population. Mechanical loading was simulated through a simplified finite element model aimed at isolating rib shape from other factors influencing mechanical response. Four loading scenarios were used representing idealized free and constrained loading conditions in axial (body-anterior) and lateral directions. Characteristic rib stiffness and maximum stress location were tracked as simulation output measures. Regression models of rib stiffness found that all shape model parameters added information when predicting stiffness under each loading condition, with their linear combination able to account for 95% of the population stiffness variation due to shape in midlevel ribs for free axial loading, and 92%-98% in other conditions. Full regression models including interactive terms explained up to 99% of population variability. Results allow researchers to better evaluate the differences in stiffness results that are obtained from physical testing by providing a framework with which to explain variation due to rib shape.
authors.affiliation: Department of Biomedical Engineering, University of Michigan.|International Center for Automotive Medicine, University of Michigan.
authors.forename: Sven A
authors.initials: SA
authors.lastname: Holcombe
authors.affiliation: International Center for Automotive Medicine, University of Michigan.
authors.forename: Stewart C
authors.initials: SC
authors.lastname: Wang
authors.affiliation: Department of Biomedical Engineering, University of Michigan.
authors.forename: James B
authors.initials: JB
authors.lastname: Grotberg
mesh_terms: D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D004548:Elasticity; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D012044:Regression Analysis; D012253:Rib Fractures; D012272:Ribs / Q000000981:diagnostic imaging*; D013314:Stress, Mechanical; D013898:Thoracic Injuries; D014057:Tomography, X-Ray Computed; D016474:Weight-Bearing; D055815:Young Adult