Effects of exogenous crosslinking on in vitro tensile and compressive moduli of lumbar intervertebral discs
Received 19 April 2005; accepted 9 August 2006. published online 27 September 2006.
Abstract
Background
Collagen crosslinks may play a vital role in preventing ongoing disc degeneration. Age-accumulating crosslinks have been thought to increase brittleness and reduce fatigue resistance. However recent studies have demonstrated increases in fatigue resistance, joint stability and nutritional flow properties resulting from crosslink augmentation. In this study, multi-directional moduli of bovine lumbar intervertebral discs were measured in vitro, including circumferential tension, radial compression, axial tension, and axial compression in control and crosslinked specimens.
Methods
Four types of annulus fibrosus specimens were dissected from control and crosslinked discs. Cross-sectional areas were measured using a non-contact laser measurement system and then four separate mechanical tests were conducted using a materials testing machine with custom-made loading fixtures.
Findings
The circumferential specimens demonstrated the highest moduli in both low stiffness and linear elastic regions. After a crosslink treatment, the modulus increased more in circumferential tension compared to axial tension and more in axial compression compared to radial compression. Other tensile properties had higher increases in circumferential tension compared to axial tension after crosslinking.
Interpretation
Assuming form follows function, circumferential tension is the predominant type of stress experienced by non-degenerated annulus fibrosus. The anisotropic mechanical properties of the annulus fibrosus is non-uniformly affected by crosslink augmentation. Dominant effects were in the directions with greater inherent stiffnesses. These results suggest some beneficial effects of crosslink augmentation on the mechanical properties of the annulus fibrosus: increase in ultimate strength, yield strength, toughness, and modulus in the principal stress directions.
aDepartment of Orthopaedic Surgery, Tri-Service General Hospital, No. 325, Sec. 2, Chenggong Road, Neihu District, Taipei City, Taipei 114, Taiwan
bUniversity of California Los Angeles, Department of Organismic Biology, Ecology, & Evolution, 621 Charles E. Young Dr. South, Los Angeles, CA 90095-1606, USA
cInstitute for Spinal Disorders, Cedars-Sinai Medical Center, 8700 Beverly Blvd., Davis Research Building, 6th Floor, Room D-6068, Los Angeles, CA 90048, USA
ABSTRACT