Trainee Lightning Talk: Neilish Frings

Biomechanical, Structural, and Composition Characterization of the Vertebra-Disc Interface

ABSTRACT

The vertebral endplate region, consisting of the cartilage endplate (CEP), bony endplate (BEP), and subchondral trabecular bone (STB), forms the junction between the intervertebral disc and vertebral body. The goal of this study was to characterize the mechanical, structural, and composition properties of the endplate region across age and disc degeneration (DD), and to compare these properties among the different components of the region.

Cadaver lumbar spine segments (n=45) were imaged with MRI to evaluate DD, and two CEP, BEP, and STB samples (one each from the superior and inferior halves of the vertebra) were dissected from each specimen. CEP samples were mechanically tested in confined compression to measure properties including the percent relaxation. BEP samples were imaged with microCT to measure microstructure and subjected to a four-point bend test to assess mechanical properties. Ash analysis was then carried out on BEP and STB samples to measure composition.

Mechanical, structural, and compositional properties of the endplate region were not dependent on age or DD (p>0.002). The composition of BEP and STB samples differed, with BEP samples having lower ash fraction (p<0.001) and water content (p=0.001) and higher organic content (p<0.001). In superior endplates, CEP relaxation decreased with BEP thickness (p=0.011); in inferior endplates, CEP relaxation decreased with BEP BV/TV (p=0.023).

Our results indicate that age and DD are not reliable indicators of endplate properties, suggesting a need for further development and adoption of clinically feasible methods for characterizing the structure and composition of the tissues in this region. Our findings of differences in composition between the BEP and STB highlight this need, as many studies of vertebral bone include the STB but not BEP. Correspondence was found between CEP and BEP properties relating to transport, indicating that samples with a more permeable BEP are also likely to have a more permeable CEP, together increasing transport to and from the disc.

Neilesh R. Frings^1,3, Harrah R. Newman⁴, Faysal M. Haque⁴, Dawn M. Elliott⁴, Elise F. Morgan^1,2,3

¹Biomedical Engineering Department, Boston University, Boston, MA, ²Mechanical Engineering Department, Boston University, Boston, MA, ³Center for Multiscale and Translational Mechanobiology, Boston University, Boston, MA, ⁴Biomedical Engineering Department, University of Delaware, Newark, DE