Human Disc Degeneration Is Accompanied by a Loss of Anterior Annulus Fibrosus Interlamellar Matrix Integrity as Assessed by Peel Tests

Abstract

Introduction

Disc degeneration (DD) is accompanied by biomechanical changes in the intervertebral discs. The lamellae of the annulus fibrosus (AF) are interconnected through the interlamellar matrix (ILM). The ILM contains interlamellar cross-bridges, connecting the lamellae radially in three dimensions. Weakening of the ILM and the cross-bridges could contribute to delamination between the lamellae, reducing their ability to resist loads and thus contributing to loss of AF integrity associated with the development and progression of degeneration. The objective of the present study was to quantify the differences in interlamellar mechanical properties of fresh AF samples from surgical DD individuals compared to AF samples from non-DD donors.

Methods

An interlamellar peel test was performed on fresh AF tissue collected from DD surgeries (n = 36) and non-DD organ donors (n = 13). The tissue was peeled at 0.5 mm/s until complete separation. Interlamellar mechanical properties were calculated from the force-displacement curve.

Results

Samples from DD individuals had lower Peel Stiffness (p = 0.001), Peel Strength (p = 0.001), Peel Toughness (p = 0.0009), and Standard Deviation of the Peel Stress (p = 0.02) compared to the tissue from non-DD organ donors. Age had moderate negative correlations with Peel Stiffness (R = −0.59), Peel Strength (R = −0.66), and Peel Toughness (R = −0.69) for non-DD samples only.

Discussion

The mechanical integrity of the ILM was determined to be lower in surgical DD individuals compared to non-DD donors. Aging alone may not have affected the results, and rather, loss of the integrity of ILM during disease progression appeared to have significantly contributed to the differences observed. This study provides new mechanical insights into the delamination often observed in the AF of surgical DD individuals. Future biochemical and immunolocalization studies, integrated with mechanical data, will aim to understand the role of collagen and elastin structure and composition in the decreased mechanical integrity of affected tissues.