REGIONAL VARIATION IN TENSILE PROPERTIES AND BIOCHEMICAL-COMPOSITION OF THE HUMAN LUMBAR ANULUS FIBROSUS

Study Design. The structure-function relationship of anulus fibrosus o f nondegenerate lumbar intervertebral discs was investigated. Objectiv es. The tensile properties and biochemical composition of single lamel la specimens from human anulus fibrosus and their variations with anat omic region were determined. Summary of Background Data. Regional diff erences in composition and ultrastructure suggest differences in tensi le properties. Methods. Single lamella specimens were isolated from th e anulus, equilibrated in 0.15 mol/L NaCl and tested in uniaxial tensi on using a slow strain-rate protocol. Adjacent specimens were used to determine biochemical composition (including hydration, collagen, prot eoglycan, and hydroxypyridinium crosslink density). Tensile properties , biochemical composition, and anatomic location were compared. Result s. Significant radial and circumferential variations in tensile proper ties of anulus were detected, with the anterior being stiffer than the posterolateral regions, and the outer being stiffer than the inner re gions. Conclusions. The regional differences in tensile properties may result predominantly from structural rather than compositional variat ions and may contribute to the clinical frequency of anulus failure in the posterolateral region.