The Journal of Bone and Joint Surgery (American). 2006;88:47-51.
doi:10.2106/JBJS.F.00035
© 2006 The Journal of Bone and Joint Surgery, Inc.
Cell Deformation and Micromechanical Environment in the Intervertebral Disc
Neil A. Duncan, BEng, PhD
Corresponding author: Neil A. Duncan, BEng, PhD Schulich School of
Engineering, University of Calgary, 2500 University Drive N.W., Calgary,
Alberta T2N 1N4, Canada. E-mail address:
duncan{at}ucalgary.ca
In support of his research for or preparation of this manuscript, the
author received grants or outside funding from the Canadian Institutes of
Health Research, the Canada Research Chair in Orthopaedic Bioengineering, the
Canadian Foundation for Innovation, the Natural Sciences and Engineering
Research Council, and the Whitaker Foundation. The author did not receive
payments or other benefits or a commitment or agreement to provide such
benefits from a commercial entity. No commercial entity paid or directed, or
agreed to pay or direct, any benefits to any research fund, foundation,
educational institution, or other charitable or nonprofit organization with
which the author is affiliated or associated.
NOTE: The author acknowledges his colleagues, Drs. J.R. Matyas
and J.B. Rattner, for their close collaboration; graduate students Dr. S.B.
Bruehlmann, P. Hulme, E. Kelly, and M. van der Werf, who were involved in this
research and who were so essential to conducting the biomedical engineering
research.
The purpose of this research was to explore the in situ anatomic and
mechanical environment of disc cells. Laser scanning confocal microscopy was
used to characterize three-dimensional morphology of intervertebral disc
cells, micromechanical deformation and interaction with extracellular matrix,
and functional intercellular communication. Bovine coccygeal discs were used
for both the anatomic and micromechanical investigations.
Anulus fibrosus cells had a complex morphology with sinuous processes woven
into the extracellular matrix, particularly in the outer aspect of the anulus
where they were also interconnected via functional gap junctions. They were
also found in an extensive pericellular matrix of type-VI collagen, joining as
many as ten cells into linear cell arrays that could be extracted from the
matrix as functional units. Mechanically, collagen fibril sliding was
demonstrated to govern cell mechanics and strain transfer in the anulus
fibrosus during loading activities. Lamellar cells were largely protected from
direct tensile strains in the matrix, with minimal intercellular strains.
However, intercellular strains between lamellar cells in adjacent arrays were
large, illustrating shearing between linear cell arrays. Appreciable shear was
observed across the lamellar cell bodies as well as to the cellular processes
woven into the matrix. These findings demonstrated the morphologic and
micromechanical complexity of anulus fibrosus cells. The knowledge of the in
situ environment of disc cells will provide a base to investigate the
mechanical implications of disc degeneration on the cellular environment and
to better understand how mechanical and genetic risk factors can impact the
cells that are essential to maintaining the intervertebral disc.

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