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research-article

Evaluation and Prediction of Human Lumbar Vertebrae Endplate Mechanical Properties Using Indentation and Computed Tomography

[+] Author and Article Information
Ravi Patel

Department of Mechanical Engineering, University of Colorado Denver, Denver, CO, USA; Department of Mechanical Engineering, Campus Box 112, PO Box 173364, Denver, CO 80217
ravi.patel@ucdenver.edu

Andriy Noshchenko

Department of Orthopedics, University of Colorado Anschutz Medical Campus, Aurora, CO, USA; Department of Orthopedics, 13001 E 17th Ave., Building 500, Mail Stop 432, Aurora, CO 80045
andriy.noshchenko@ucdenver.edu

R. Dana Carpenter

Department of Mechanical Engineering, University of Colorado Denver, Denver, CO, USA; Department of Mechanical Engineering, Campus Box 112, PO Box 173364, Denver, CO 80217
dana.carpenter@ucdenver.edu

Todd Baldini

Department of Orthopedics, University of Colorado Anschutz Medical Campus, Aurora, CO, USA; Department of Orthopedics, 13001 E 17th Ave., Building 500, Mail Stop 432, Aurora, CO 80045
todd.baldini@ucdenver.edu

Carl Frick

Department of Mechanical Engineering, University of Wyoming, Laramie, WY, USA; College of Engineering and Applied Science, Department of Mechanical Engineering, Dept. 3295, 1000 E. University Avenue, Laramie, WY 82071
cfrick@uwyo.edu

Vikas V. Patel

Department of Orthopedics, University of Colorado Anschutz Medical Campus, Aurora, CO, USA; 12631 E. 17th Avenue, Academic Office 1, Room 4602, Denver, CO 80045
vikas.patel@ucdenver.edu

Christopher Yakacki

Department of Mechanical Engineering, University of Colorado Denver, Denver, CO, USA; Department of Mechanical Engineering, Campus Box 112, PO Box 173364, Denver, CO 80217
chris.yakacki@ucdenver.edu

1Corresponding author.

ASME doi:10.1115/1.4040252 History: Received February 09, 2018; Revised May 07, 2018

Abstract

Current implant materials and designs used in spinal fusion show high rates of subsidence. There is currently a need for a method to predict the mechanical properties of the endplate using clinically available tools. The purpose of this study was to develop a predictive model of the mechanical properties of the vertebral endplate at a scale relevant to the evaluation of current medical implant designs and materials. Twenty vertebrae (10 L1 and 10 L2) from 10 cadavers were studied using dual-energy x-ray absorptiometry (DEXA) to define bone status (normal, osteopenic, or osteoporotic) and CT to study endplate thickness (┬Ám), density (mg/mm3), and mineral density of underlying trabecular bone (mg/mm3) at discrete sites. Apparent Oliver-Pharr modulus, stiffness, maximum tolerable pressure, and Brinell hardness were measured at each site using a 3mm spherical indenter. Predictive models were built for each measured property using various measures obtained from CT and demographic data. Stiffness showed a strong correlation between the predictive model and experimental values (r=.85), a polynomial model for Brinell Hardness had a stronger predictive ability compared to the linear model (r=.82), and the modulus model showed weak predictive ability (r=.44), likely due the low indentation depth and the inability to image the endplate at that depth (~0.15mm). Osteoporosis and osteopenia were found to be the largest confounders of the measured properties, decreasing them by approximately 50%. It was confirmed that vertebral endplate mechanical properties could be predicted using CT and demographic indices.

Copyright (c) 2018 by ASME
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