The effect of disc degeneration on the structural property distributions in the cervical vertebral endplates

Objective To study the effect of disc degeneration on the structural property distributions in the cervical vertebral endplates. Methods A 2 mm diameter hemispherical indenter was used to perform indentation tests at 0.03 mm/s to the depth of 2 mm at 20 normalized locations in 50 bony endplates of intact human cervical vertebrae (C 2～C 7). The resulting load displacement curves were used to extract the failure load and stiffness of each test site. Grade of disc degeneration was determined using Nachemson′s grading scale. One way ANOVA, factorial analyses, SNK tests and correlate analyses were used to analyze the result data. Results Both the failure load and stiffness decreased with disc degeneration in the cervical endplates ( P 0 001, both), and correlated significantly with the disc degeneration ( r s=-0 429 and r s=-0 244, respectively). Only the distribution of superior cervical endplate changed with disc degeneration, but that of inferior cervical endplate changed little. Conclusions The structural property distributions in the cervical vertebral endplates change significantly in the degenerated discs. It suggests that disc degeneration is an important factor to evaluate the intervertebral implant subsidence in anterior cervical fusion.