Effects of exogenous crosslinking on in vitro tensile and compressive moduli of lumbar intervertebral discs.
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.


RESULTS
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.


CONCLUSIONS
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.
Chuang
Shih-Youeng
SY
Department of Orthopaedic Surgery, Tri-Service General Hospital, No. 325 Sec. 2 Chenggong Road, Neihu District, Taipei City, Taipei 114, Taiwan. shihyouc@hotmail.com
Odono
Russell M
RM
Hedman
Thomas P
TP
D000818:Animals; D001696:Biomechanical Phenomena; D002417:Cattle; D019245:Compressive Strength; D003432:Cross-Linking Reagents / Q000494:pharmacology; D066298:In Vitro Techniques; D007403:Intervertebral Disc / Q000473:pathology*; D008159:Lumbar Vertebrae / Q000378:metabolism; D008161:Lumbosacral Region; D008954:Models, Biological; D013314:Stress, Mechanical; D013718:Tensile Strength; D016474:Weight-Bearing
D003432:Cross-Linking Reagents