Micromechanics of the human vertebral body for forward flexion.
To provide mechanistic insight into the etiology of osteoporotic wedge fractures, we investigated the spatial distribution of tissue at the highest risk of initial failure within the human vertebral body for both forward flexion and uniform compression loading conditions. Micro-CT-based linear elastic finite element analysis was used to virtually load 22 human T9 vertebral bodies in either 5° of forward flexion or uniform compression; we also ran analyses replacing the simulated compliant disc (E=8 MPa) with stiff polymethylmethacrylate (PMMA, E=2500 MPa). As expected, we found that, compared to uniform compression, forward flexion increased the overall endplate axial load on the anterior half of the vertebra and shifted the spatial distribution of high-risk tissue within the vertebra towards the anterior aspect of the vertebral body. However, despite that shift, the high-risk tissue remained primarily within the central regions of the trabecular bone and endplates, and forward flexion only slightly altered the ratio of cortical-to-trabecular load sharing at the mid-vertebral level (mean±SD for n=22: 41.3±7.4% compression; 44.1±8.2% forward flexion). When the compliant disc was replaced with PMMA, the anterior shift of high-risk tissue was much more severe. We conclude that, for a compliant disc, a moderate degree of forward flexion does not appreciably alter the spatial distribution of stress within the vertebral body.
Orthopaedic Biomechanics Laboratory, Department of Mechanical Engineering, University of California, Berkeley, CA 94720-1740, USA. haisheng@me.berkeley.edu
Haisheng
H
Yang
Shashank
S
Nawathe
Aaron J
AJ
Fields
Tony M
TM
Keaveny
D019245:Compressive Strength; D006801:Humans; D007403:Intervertebral Disc / Q000000981:diagnostic imaging / Q000293:injuries / Q000503:physiopathology*; D008954:Models, Biological; D010024:Osteoporosis / Q000000981:diagnostic imaging / Q000503:physiopathology*; D019904:Polymethyl Methacrylate / Q000737:chemistry; D011859:Radiography; D016103:Spinal Fractures / Q000000981:diagnostic imaging / Q000503:physiopathology*; D016474:Weight-Bearing
D019904:Polymethyl Methacrylate