ISSLS prize winner: mechanical influences in progressive intervertebral disc degeneration

Stefanakis, M, Luo, Jin ORCID: https://orcid.org/0000-0001-5451-9535, Pollintine, P, Dolan, P and Adams, MA (2014) ISSLS prize winner: mechanical influences in progressive intervertebral disc degeneration. Spine, 39 (17). pp. 1365-1372. ISSN 0362-2436

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Abstract

Study Design.

Mechanical study on cadaver motion segments.

Objective.

To determine whether high gradients of compressive stress within the intervertebral disc are associated with progressive disc degeneration.
Summary of Background Data.

Mechanical loading can initiate disc degeneration but may be unimportant in disease progression, because degenerative changes cause the disc to be increasingly “stress-shielded” by the neural arch. However, the most typical feature of advanced disc degeneration (delamination and collapse of the annulus) may not depend on absolute values of compressive stress but on gradients of compressive stress that act to shear annulus lamellae.

Methods.

A total of 191 motion segments (T7–T8 to L5–S1) were dissected from 42 cadavers aged 19 to 92 years. Each was subjected to approximately 1 kN compression, while intradiscal stresses were measured by pulling a pressure transducer along the disc's midsagittal diameter. “Stress gradients” in the annulus were quantified as the average rate of increase in compressive stress (MPa/mm) between the nucleus and the region of maximum stress in the anterior or posterior annulus. Measurements were repeated before and after creep loading and in simulated flexed and erect postures. Disc degeneration was assessed macroscopically on a scale of 1 to 4.

Results.

As grade of disc degeneration increased from 2 to 4, nucleus pressure decreased by an average 68%, and maximum compressive stress in the annulus decreased by 48% to 64%, depending on location and posture. In contrast, stress gradients in the annulus increased by an average 75% in the anterior annulus (in flexed posture) and by 108% in the posterior annulus (in erect posture). Spearman rank correlation showed that these increases were statistically significant.

Conclusion.

Despite stress-shielding by the neural arch, gradients of compressive stress increase with increasing grade of disc degeneration. Stress gradients act to shear adjacent lamellae and can explain progressive annulus delamination and collapse.

Level of Evidence: N/A

Item Type: Article
Uncontrolled Keywords: disc degeneration; delamination; progression; cadaveric; motion segments; stress gradient; shear; nucleus pressure; annulus compressive stress; stress-shielding.
Subjects: Construction and engineering > Biomedical engineering
Medicine and health
Medicine and health > Physiology
Related URLs:
Depositing User: Jin Luo
Date Deposited: 08 May 2020 15:49
Last Modified: 08 May 2020 23:08
URI: http://repository.uwl.ac.uk/id/eprint/6903

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