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Alterations in the mechanical behavior of the human lumbar nucleus pulposus with degeneration and aging
Author(s) -
Iatridis James C.,
Setton Lori A.,
Weidenbaum Mark,
Mow Van C.
Publication year - 1997
Publication title -
journal of orthopaedic research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.041
H-Index - 155
eISSN - 1554-527X
pISSN - 0736-0266
DOI - 10.1002/jor.1100150224
Subject(s) - viscoelasticity , nucleus , degeneration (medical) , materials science , relaxation (psychology) , stress relaxation , shear (geology) , shear modulus , anatomy , composite material , pathology , medicine , creep , biology , neuroscience
Abstract This study tested the hypothesis that changes in the morphology and composition of the nucleus pulposus with age and degeneration have associated changes in its mechanical properties. A torsional shear experiment was used to determine viscoelastic shear properties of cylindrical samples of human nucleus pulposus with large ranges of grades of morphological degeneration (normal to severely degenerated) and ages (range: 16–88 years; average: 57 ± 21.5 years). Viscoclastic shear properties were determined from stress‐relaxation and dynamic sinusoidal tests. A linear viscoelastic law with a variable‐amplitude relaxation spectrum was used to model experimental behaviors of nucleus pulposus specimens. A statistically significant increase in the instantaneous and dynamic shear moduli was found with increasing age and grade of degeneration; the values for moduli ranged from 5.0 to 60 kPa. A significant decrease in tanδ was also detected; the values ranged from 0.43 to 0.33, indicating a decreased capacity for the nucleus pulposus to dissipate energy. The dynamic modulus and tanδ were also significantly affected by frequency. It was generally concluded that the nucleus pulposus undergoes a transition from “fluid‐like” behavior to more “solid‐like” behavior with aging and degeneration.