Regional variation in tensile properties and biochemical composition of the human lumbar anulus fibrosus.

Abstract

The structure-function relationship of anulus fibrosus of nondegenerate lumbar intervertebral discs was investigated. The tensile properties and biochemical composition of single lamella specimens from human anulus fibrosus and their variations with anatomic region were determined. Regional differences in composition and ultrastructure suggest differences in tensile properties. Single lamella specimens were isolated from the anulus, equilibrated in 0.15 mol/L NaCl and tested in uniaxial tension using a slow strain-rate protocol. Adjacent specimens were used to determine biochemical composition (including hydration, collagen, proteoglycan, and hydroxypyridinium crosslink density). Tensile properties, biochemical composition, and anatomic location were compared. Significant radial and circumferential variations in tensile properties of anulus were detected, with the anterior being stiffer than the posterolateral regions, and the outer being stiffer than the inner regions. The regional differences in tensile properties may result predominantly from structural rather than compositional variations and may contribute to the clinical frequency of anulus failure in the posterolateral region.