Mechanical yield of the lumbar annulus: a possible contributor to instability: Laboratory investigation. J Neurosurg Spine 2014 Oct;21(4):608-13
Date
08/02/2014Pubmed ID
25084030DOI
10.3171/2014.6.SPINE13401Scopus ID
2-s2.0-84907863663 (requires institutional sign-in at Scopus site) 20 CitationsAbstract
OBJECT: Segmental instability in the lumbar spine can result from a number of mechanisms including intervertebral disc degeneration and facet joint degradation. Under traumatic circumstances, elevated loading may lead to mechanical yield of the annular fibers, which can decrease load-carrying capacity and contribute to instability. The purpose of this study was to quantify the biomechanics of intervertebral annular yield during tensile loading with respect to spinal level and anatomical region within the intervertebral disc.
METHODS: This laboratory-based study incorporated isolated lumbar spine annular specimens from younger and normal or mildly degenerated intervertebral discs. Specimens were quasi-statically distracted to failure in an environmentally controlled chamber. Stress and strain associated with yield and ultimate failure were quantified, as was stiffness in the elastic and postyield regions. Analysis of variance was used to determine statistically significant differences based on lumbar spine level, radial position, and anatomical region of the disc.
RESULTS: Annular specimens demonstrated a nonlinear response consisting of the following: toe region, linear elastic region, yield point, postyield region, and ultimate failure point. Regional dependency was identified between deep and superficial fibers. Mechanical yield was evident prior to ultimate failure in 98% of the specimens and occurred at approximately 80% and 74% of the stress and strain, respectively, to ultimate failure. Fiber modulus decreased by 34% following yield.
CONCLUSIONS: Data in this study demonstrated that yielding of intervertebral disc fibers occurs relatively early in the mechanical response of the tissues and that stiffness is considerably decreased following yield. Therefore, yielding of annular fibers may result in decreased segmental stability, contributing to accelerated degeneration of bony components and possible idiopathic pain.
Author List
Stemper BD, Baisden JL, Yoganandan N, Shender BS, Maiman DJAuthors
Brian Stemper PhD Professor in the Biomedical Engineering department at Medical College of WisconsinNarayan Yoganandan PhD Professor in the Neurosurgery department at Medical College of Wisconsin
MESH terms used to index this publication - Major topics in bold
AdultBiomechanical Phenomena
Cadaver
Humans
Intervertebral Disc
Joint Instability
Lumbar Vertebrae
Stress, Mechanical
Tensile Strength