Radial tensile properties of the lumbar annulus fibrosus are site and degeneration dependent

TLDR

The annulus fibrosus exhibits material behavior dominated by the interlaminar matrix, with tensile moduli an order of magnitude lower than those used in earlier models. The study aimed to determine whether radial tensile properties vary by disc location and degeneration level. An in‑vitro tensile test was performed on lumbar annulus fibrosus specimens to measure radial mechanical response. The stress‑strain curve was nonlinear, with mean tangent moduli of 0.19 MPa at zero strain and 0.47 MPa at 70 % yield; middle annulus layers were stiffer and failed at lower strains, while degenerated discs displayed a 30 % reduction in yield and ultimate stress relative to normal discs.

Abstract

Abstract We conducted an in vitro study of the radial tensile properties of the annulus fibrosus. The stress‐strain response was nonlinear, with a mean tangent modulus of 0.19 MPa at zero strain and 0.47 MPa at 70% of the yield strain. We also investigated whether these properties varied as a function of location within the disc and degree of degeneration. Specimens harvested from the middle layers of the annulus were stiffer and failed at smaller strain magnitudes than those from the inner or outer annulus (analysis of covariance, p <0.05). Differences due to degeneration were evident; degenerated discs had a 30% decrease in yield and ultimate stress compared with normal discs. Similarity between our data and those reported for the annulus in compression suggests that these values reflect the material behavior of the interlaminar matrix and are an order of magnitude smaller than values used in previous analytical representations of this tissue. We expect that awareness of these data will result in improved understanding of the physical behavior and tolerance to injury of the annulus fibrosus.