Effect of Fatigue and Rest on the Rheological Properties of Intact Intervertebral Disc
Date Issued
2008
Date
2008
Author(s)
Lin, Tzu-Cheng
Abstract
Objective: To evaluate the effect of the duration of fatigue loading and the rest on the rheological properties of healthy porcine intervertebral disc.ummary of Background Data: Fatigue loading can induce the low back pain by altering the water content and viscoelastic behaviors of the intervertebral disc. Long term fatigue loading was suspected to result in changes of material properties due to the irreversible failure. However, the mechanical properties of disc fluid flow (i.e., the rheology) within the disc have not been fully discussed yet. The understanding of effect of fatigue loading and rest on the disc rheological properties can be beneficial to delineate the mechanism of fatigue loading induced spinal disorders.ethods: Ten porcine lumbar motion segments (L1-L2，L3-L4) without posterior elements were applied with fatigue loading (190~590N) at 5 Hz for 0.5, 1, 2, 3, and 4 hours (9,000, 18,000, 36,000, 54,000, 72,000 cycles), respectively. A creep test using 420 N was applied after a 24 hours saline immersion post fatigue loading. The axial deformation during creep phase was curve-fitted with linear biphasic model to obtain the aggregate modulus (HA) and permeability coefficient (k). After the fatigue loading, the disc was sectioned along sagittal and coronal plane to find the structure changes of anulus fibrosus and nucleus pulposus. The paired-t test was performed to evaluate the change of disc height, HA, and k after a series of fatigue loading and 24 hours rest. esults: The height of intervertebral disc was not recovered by a 24 hours rest after fatigue loading. The permeability decreased significantly with the duration of fatigue loading, while the aggregate modulus remained the same. The ruptured inner fibrosus were found after fatigue loading. onclusion: A 24 hours rest is not able to fully restore the fluid loss during fatigue loading. The increase of duration of the fatigue loading reduces the disc permeability and damages the structure of inner anular fibrosus.
Subjects
disc
fatigue
creep test
permeability
aggregate modulus
Type
thesis
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