Effect of Nucleus Pulposus Denaturation andxogenous Crosslinking on the Dynamic Properties of Intervertebral Disc
Date Issued
2009
Date
2009
Author(s)
Yang, Sung-Min
Abstract
Objective: The purpose of this study is to evaluate the effect of nucleus denaturation and exogenous crosslinking on disc dynamic properties. ummary of Background Data: Fatigue loading can damage disc structure integrity. In early stage of tissue healing post disc injury, disc matrix crosslinkings, especially nucleus pulposus, are denatured by disc enzymes. In the following subacute stage, new crosslinking forms with the growth of fibrosis tissue from the injured sites. Howerer, the interaction of nucleus denaturation and crosslinking generation with the disc dynamic properties remains unclear.ethods: In total of 45 porcine lumbar body-disc-body constructs (L1-L2, L3-L4) were assigned to “nucleus pulposus (NP) denaturation protocol” (n=27) and “anular fibrosus (AF) damage protocol” (n=18). For the “NP denaturation protocol”, 9 specimens were selected as “healthy discs”, receiving no injection, and applied with a 30 min fatigue loadings twice. These discs rehydrated in saline solution for 24 hr before and after the first fatigue loading. The other 18 specimens were injected with 1ml trypsin solution, immersed in saline solution for 24 hr and then loaded with a 30 min fatigue loading. After the fatigue loading, 9 discs out of these 18 specimens were immersed in saline bath for 24 hr, while the other 9 discs were injected with 1ml 0.33% genipin solution before saline bath immersion. Each disc was then loaded with another 30 min fatigue loading. An impulse test was applied to every disc in NP-denatured group at 0, 10, 20, and 30 min of second fatigue loading. For the “AF damage protocol”, each specimen was loaded with 2 hr fatigue loading first, followed by a 24 hr rest, and then applied with another 2 hr fatigue loading. After the first 2 hr fatigue loading, 9 specimens were immersed in saline bath, while the other 9 specimens were immersed in 0.33% genipin solution. During the second 2 hr fatigue loading, an impulse test was applied at time point of 0, 0.5, 1, and 2 hr. The stiffness (K, N/mm) and damping coefficient (C, Ns/mm) of disc was calculated using the one-dimension spring-damping model and impulse test loading information.esults: (1) NP denaturation protocol: compared to the healthy disc, NP denaturation did not change the disc stiffness but significantly decreased the damping coefficient (P= 0.000) at the end of fatigue loading. NP degeneration also increased the change rate of disc stiffness and damping coefficient with the fatigue loading time. In comparison with the NP-denatured disc, after crosslinking generation the disc stiffness significantly decreased (P= 0.024) but the damping coefficient significantly increased (P= 0.024) at the end of fatigue loading. The change rates of disc stiffness and damping coefficient was the same as those of healthy discs. (2) AF damage protocol: the disc stiffness and damping coefficient reached plateau at 1 hr of the first fatigue loading but at 0.5 hr of the second fatigue loading. The plateau value of disc stiffness and damping coefficient were the same comparing the first and the second fatigue loading. After crosslinking, the disc stiffness and damping coefficient reached plateau at 1 hr of the second fatigue loading. The plateau value of disc stiffness significantly decreased (P= 0.042), while that of damping coefficient was not changed. onclusion: Faster fluid outflows during fatigue loading is caused by both of NP denaturation and AF damage based on the increased change rate of disc dynamic properties. Disc damping coefficient decreases after NP denaturation and recovers after crosslinking generation in NP, indicating positive relation between shock attenuation capacity and NP crosslinking level. The crosslinking generation in disc decreases disc stiffness, reducing disc strength to external loading.
Subjects
disc injury
matrix denaturation
crosslinking
dynamic properties
Type
thesis
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