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ISSLS Prize Winner: Microstructure and Mechanical Disruption of the Lumbar Disc Annulus: Part I: A Microscopic Investigation of the Translamellar Bridging Network

Schollum, Meredith L., BE*; Robertson, Peter A., MD; Broom, Neil D., PhD*

doi: 10.1097/BRS.0b013e31817bb92c
Basic Science

Study Design. Microstructural investigation of interlamellar connectivity.

Objective. To reveal the macro and micro structure of the translamellar bridging network in the lumbar annulus.

Summary of Background Data. Contrary to the view that there is minimal interconnection between lamellar sheets, experimental data reveal a significant contribution to the material behavior of the annulus from interactions between fiber populations of alternating lamellae. Recent microstructural studies indicate a localized rather than a homogeneous or dispersed mode of interconnectivity between lamellae.

Methods. Anterior segments of ovine lumbar discs in 2 age groups were sectioned along the oblique fiber angle. A 3-dimensional picture of the translamellar bridging network is developed using structural information obtained from fully hydrated unstained serial sections imaged by differential interference contrast optics.

Results. A high level of connectivity between apparently disparate bridging elements was revealed. The extended form of the bridging network is that of occasional substantial radial connections spanning many lamellae with a subsidiary fine branching network. The fibrous bridging network is highly integrated with the lamellae architecture via a collagen-based system of interconnectivity.

Conclusion. This study demonstrates a far greater complexity to the interlamellar architecture of the disc annulus than has previously been recognized. Our findings are clearly relevant to disc biomechanics. Significant degrading of the translamellar bridging network may result in annular weakening leading potentially to disc failure. Most importantly this work opens the way to a much clearer understanding of the microanatomy of the disc wall.

The systematic analysis of fully hydrated serial slices has confirmed the presence of a collagen-based radial bridging network that both branches and weaves its way across the disc wall and is highly integrated with the alternating lamellar architecture.

From the *Department of Chemical and Materials Engineering, University of Auckland; and †Department of Orthopaedic Surgery, Auckland Hospital, Auckland, New Zealand.

Acknowledgment date: October 12, 2007. First revision date: January 22, 2008. Acceptance date: February 11, 2008.

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

Institutional 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.

Supported by the award of a University of Auckland Doctoral Scholarship (to M.L.S.).

Address correspondence and reprint requests to Neil D. Broom, PhD, Biomaterials Laboratory, Department of Chemical and Materials Engineering, The University of Auckland, Private Bag 92019, Auckland City, New Zealand; E-mail:

© 2008 Lippincott Williams & Wilkins, Inc.