Study Design. Biomechanical and radiographical study.
Objective. To test the hypothesis that stiffness and strength at discrete sites of human lumbar vertebrae depend on the 3-dimentional structure and density of the vertebral-body bone elements, and can be evaluated using models based on vertebral bone characteristics obtained from quantitative computed tomogrphy.
Summary of Background Data. We have not found published methods that allow in vivo evaluation of bone mechanical properties at discrete sites of vertebral body applicable for clinical use.
We hypothesize that human lumbar vertebral strength topography depends on the local 3-dimensional structural features of the bone structure, and that the stiffness and strength can be evaluated at discrete sites using models based on data obtained from quantitative computed tomographic (CT) images.
Methods. Forty-eight vertebrae (8 L1, 8 L2, 8 L3, 10 L4, and 14 L5) from 14 cadaveric subjects (9 men and 5 women; age, 43–99 yr) were studied. Stiffness (modulus of elasticity) and strength (maximum load and maximum tolerable pressure) were defined by an indentation test at 11 discrete sites on the cranial and caudal surfaces of each vertebral endplate. Before the indentation test radiography, dual-energy x-ray absorptiometry, micro-CT, and conventional-CT (con-CT) of the vertebrae were performed. Micro-CT characteristics of cortical and cancellous bones of 18 vertebrae were measured at each region of interest defined by a 3-dimensional coordinate system. The most informative indices regarding endplate strength were selected by correlation analysis. Predictive models of local stiffness and strength were created using selected indices obtained by micro-CT and con-CT (40 vertebrae) images.
Results. Local stiffness and strength of the tested specimens were highly variable. Endplate thickness and density in combination with adjacent trabecular bone density, existence of endplate defects, and subject's age were good predictors of local stiffness and strength, applicable for con-CT. Polynomial multiple regression of these characteristics provides the best correlation with stiffness (r2 = 0.82; P < 0.001) and strength (r2 = 0.74).
Conclusion. Stiffness and strength at discrete sites of human lumbar vertebrae depend on the superficial vertebral bone structure and density and can be evaluated using models based on quantitative analysis of micro-CT and con-CT images.
Bone mechanical properties, and structural and densitometry characteristics were studied at discrete sites of cranial and caudal surfaces of human lumbar vertebrae obtained from aged cadaveric subjects. Predictive models based on microcomputed tomography and conventional computed tomographic characteristics allow indirect evaluation of stiffness and strength at discrete sites of lumbar vertebral surfaces.
*Spine Center, Department of Orthopaedics
†Department of Mechanical Engineering, College of Engineering and Applied Science, and
‡Bioengineering Division, Department of Orthopaedics, University of Colorado, Denver, CO.
Address correspondence and reprint requests to Andriy Noshchenko, PhD, Department of Orthopaedics, University of Colorado-Denver, 12631 E 17th Ave, Rm 4510, Mail Stop B202, PO Box 6511, Aurora, CO 80045; E-mail: Andriy.Noshchenko@ucdenver.edu
Acknowledgment date: January 19, 2012. Revision date: June 14, 2012. Acceptance date: July 23, 2012.
The device(s)/drug(s) is/are FDA-approved or approved by corresponding national agency for this indication.
No funds were received in support of this work.
One or more of the author(s) has/have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this manuscript: for example, honoraria, gifts, consultancies, royalties, stocks, stock options, decision-making position.