The relation between vertebral endplate shape and lumbar disc herniations.

STUDY DESIGN: Blinded review of selected and un-selected computed tomographic myelograms. OBJECTIVE: To determine whether shape of the vertebral body endplate margins is a risk factor for the development of symptomatic lumbar disc herniations. 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 could apply to the lumbar spine because of to the cylindrical shape of the lumbar disc and its high water content in nonelderly individuals. It was further hypothesized that differences in the radius of the curvature could place stresses on the anulus that would make posterior disc herniations more likely with "rounder" endplates. METHODS: Ninety-seven contrast computed tomography scans were reviewed at transitional L4-L5 and L5-S1 in patients under 60 years of age, without previous spine surgery and without spondylolisthesis. Determinations of disc herniations and measurements of endplates were performed by blinded observers. A ratio of these measurements was used to determine the relative circularity of the endplate. Height, weight, body mass index, and disc endplate size 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 important factor contributing to the development of disc herniations at L4-L5 and L5-S1.