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Elastin Content Correlates With Human Disc Degeneration in the Anulus Fibrosus and Nucleus Pulposus

Cloyd, Jordan M., BA; Elliott, Dawn M., PhD

doi: 10.1097/BRS.0b013e3181132a9d
Basic Science
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Study Design. Quantitative study of elastin content in nondegenerate and degenerate human intervertebral discs.

Objective. To measure the site-specific changes in elastin content that accompany disc degeneration using a quantitative, dye-binding assay to assess elastin levels.

Summary of Background Data. Recently, an abundant and organized network of elastic fibers was observed in nondegenerated human disc using immunostaining histochemistry, suggesting a functional role for elastin. While degenerative changes in the disc extracellular matrix composition are well known, changes in elastin content that may accompany degeneration have not been reported.

Methods. Human discs were assigned a degenerative grade by 3 independent orthopedic surgeons based on gross morphology. Samples were taken from the outer anulus fibrosus (OAF), inner AF (IAF) and nucleus pulposus (NP). Elastin content was measured using a specific, dye-binding assay and normalized to dry weight and collagen content, which was measured via a hydroxyproline assay. Samples were divided into 2 groups: nondegenerate (Grades 1–2.5) and degenerate (Grades 2.6–4.0). A 2-way analysis of variance was used to test for statistical significance where the 2 factors were disc location and degeneration. Correlations of composition with degeneration and age were analyzed.

Results. In nondegenerate tissue, elastin by dry weight was on average 2.0% ± 0.3%, and there were no differences in elastin content among the locations of OAF, IAF, or NP. With degeneration, there was a significant increase in total disc elastin per dry weight at each location. The degenerate IAF had the largest amount of elastin (9.3% ± 2.3%), significantly greater than the NP and OAF. Elastin content correlated with degenerative grade and age at each site.

Conclusion. Based on the location-dependent degenerative changes, with highest increases in the IAF, elastin may function to restore lamellar structure under radial loads that potentially cause delamination. Future work will focus on distinguishing the changes in elastin orientation with degeneration and understanding the mechanical functional role of elastin in the disc.

A quantitative, dye-binding assay was used to measure the site-specific changes in the intervertebral disc elastin content with degeneration. With degeneration, there was a significant increase in total elastin per dry weight at each site, with the highest amounts in the inner anulus fibrosus. Increased elastin may be a remodeling response to restore anulus fibrosus shape and prevent circumferential delamination.

From the McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery University of Pennsylvania, Philadelphia, PA.

Acknowledgment date: August 16, 2006. First revision date: December 5, 2006. Second revision date: January 18, 2007. Acceptance date: January 22, 2007.

The manuscript submitted does not contain information about medical device(s)/drug(s).

Federal funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Address correspondence and reprint requests to Dawn M. Elliott, PhD, University of Pennsylvania, Department of Orthopaedic Surgery, McKay Orthopaedic Research Laboratory, 424 Stemmler Hall, Philadelphia, PA 19104-6081; E-mail: delliott@mail.med.upenn.edu.

© 2007 Lippincott Williams & Wilkins, Inc.