The relation between vertebral endplate shape and lumbar disc herniations

Study Design. Blinded review of selected and unselected computed tomographi c myelograms. Objective. To determine whether shape of the vertebral body endplate margin s is a risk factor for the development of symptomatic lumbar disc herniatio ns. The law of LaPlace for a fluid-filled tube suggests that anular tension could be related to endplate shape and a propensity for disc herniation. Summary of Background Data. It was hypothesized that the law of Laplace cou ld apply to the lumbar spine because of to the cylindrical shape of the lum bar disc and its high water content in nonelderly individuals. It was furth er hypothesized that differences in the radius of the curvature could place stresses on the anulus that would make posterior disc herniations more lik ely with "rounder'' endplates. Methods. Ninety-seven contrast computed tomography scans were reviewed at t ransitional L4-L5 and L5-S1 in patients under 60 years of age, without prev ious spine surgery and without spondylolisthesis. Determinations of disc he rniations and measurements of endplates were performed by blinded observers . A ratio of these measurements was used to determine the relative circular ity of the endplate. Height, weight, body mass index, and disc endplate siz e and shape were related to the presence of disc herniation. Results. By multiple logistic regression, only endplate shape was strongly related to disc herniations. Endplate area was a less significant factor in men. Conclusions. The shape of the vertebral body margin at the endplate is an i mportant factor contributing to the development of disc herniations at L4-L 5 and L5-S1.