Altered disc mechanics in mice genetically engineered for reduced type I collagen.
METHODS
Mechanically test lumbar discs of transgenic mice in compression-tension and torsion.


OBJECTIVE
Determine if a reduction in type I collagen results in decreased disc mechanics.


BACKGROUND
Quantitative relationships between disc structure and function would improve the understanding of disc generation and are essential relationships for functional tissue engineering. The reduced type I collagen transgenic mouse has been used in structure-function studies of bone and tendon, but not intervertebral discs. Methods for testing mouse discs have recently been developed, making disc structure-function studies possible.


METHODS
Microradiographed and mechanically tested lumbar discs from control and collagen-reduced mice in both compression-tension and torsion were used. Disc area and polar moment of inertia were determined from radiographic data, stiffness from mechanical data, and apparent modulus from geometric and mechanical data.


RESULTS
Collagen-reduced discs had a larger area and polar moment of inertia compared to controls. The linear and torsional stiffness of collagen-reduced and control discs were not significantly different. Finally, the apparent modulus of collagen-reduced discs was significantly less than controls in compression (73% of control) and torsion (50%).


CONCLUSIONS
Compared to controls, collagen-reduced discs had reduced apparent modulus in both loading directions, suggesting that the transgenic disc tissue was mechanically inferior to controls. These results are consistent with the widely accepted functional role of type I collagen in disc mechanics, and therefore supports the use of transgenic mice to study structure-function relationships of the disc. Future work will focus on quantifying structure-function relationships related to degeneration, as well as those relevant to the design of tissue-engineered disc replacements.
Sarver
Joseph J
JJ
McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6081, USA.
Elliott
Dawn M
DM
D000818:Animals; D001696:Biomechanical Phenomena; D024042:Collagen Type I / Q000172:deficiency* / Q000235:genetics; D007403:Intervertebral Disc / Q000737:chemistry / Q000000981:diagnostic imaging / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D011312:Pressure; D011859:Radiography; D013718:Tensile Strength; D019415:Torque
D024042:Collagen Type I