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Mechanical Influences in Progressive Intervertebral Disc Degeneration.
MedLine Citation:
PMID:  24831499     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
Study Design. Mechanical study on cadaver motion segments.Objective. To determine if 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 which act to shear annulus lamellae.Methods. 191 motion segments (T8-9 to L5-S1) were dissected from 42 cadavers aged 19-92 yrs. Each was subjected to approximately 1 kN compression, while intradiscal stresses were measured by pulling a pressure transducer along the disc's mid-sagittal 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 48-64%, 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.
Authors:
Manos Stefanakis; Jin Luo; Phillip Pollintine; Patricia Dolan; Michael A Adams
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2014-5-14
Journal Detail:
Title:  Spine     Volume:  -     ISSN:  1528-1159     ISO Abbreviation:  Spine     Publication Date:  2014 May 
Date Detail:
Created Date:  2014-5-16     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  7610646     Medline TA:  Spine (Phila Pa 1976)     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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