Effects of Endplate Removal on the Structural Properties of the Lower Lumbar Vertebral Bodies

Abstract

A biomechanical investigation using indentation tests in human cadaveric lumbar vertebrae. To determine the effect of endplate removal on the structural properties across the lower lumbar vertebral bodies (L3-L5). The structural properties of the vertebral endplates exhibit substantial regional variation. In addition, several recent studies of the endplate-implant interface have suggested that the endplate is not a significant structural element. The bony endplates on the left or right side of seven intact human vertebrae (L3-L5) were removed with a high-speed burr. Indentation tests were performed at standardized test sites on both sides of the endplate using a 3-mm diameter, hemispherical indenter with a test rate of 0.2 mm/s to a depth of 3 mm. The failure load and stiffness at each site were determined from the load-displacement curves. Three-way repeated measures analyses of variance were used to analyze the resulting data for variation in the anterior-posterior and lateral directions, as well as to determine the effect of endplate removal. For the intact endplates, both the failure load and stiffness varied significantly across the endplate surfaces (P < 0.0001), with the posterolateral regions being stronger and stiffer than the central regions. With endplate removal, the mean failure load decreased to about 33% of the intact failure load, a significant drop (P = 0.04), and there was a trend toward greater decreases posteriorly (P = 0.05). With endplate removal, the mean stiffness also decreased significantly (P = 0.01), with the greater decreases occurring laterally (P = 0.04). There was a significant effect of endplate removal on the local structural characteristics of the vertebral endplate.