Are the material properties and matrix composition of equine flexor and extensor tendons determined by their functions?

Reasons for performing study: Injury to the superficial digital flexor tendon (SDFT) is common in competition horses. The SDFT contributes to locomotory efficiency by storing energy; such tendons have low safety margins. Tendons which merely position the limb, including the opposing common digital extensor tendon (CDET), are rarely injured. The current failure of strategies to prevent or effectively treat injury to the SDFT indicates the importance of understanding how it differs from tendons which are not injury-prone. Hypothesis: That the structural and material properties and matrix composition of the SDFT and CDET differ, reflecting their specific functional requirements in vivo. Methods: Forelimb tendons were harvested from 26 mature horses and loaded to failure prior to matrix composition analysis of specimens. Results: The SDFT had a significantly higher cross-sectional area, structural stiffness, failure load and failure strain and a lower elastic modulus than the CDET (P<0.0001). Conclusions: The SDFT has conflicting requirements for strength and elasticity; although as a whole it is a stiffer structure than the CDET, differences in the matrix molecular composition including water and total sulphated glycosaminoglycan contents allow it to remain more elastic as a material. Potential relevance: Further information on how the two tendons attain these different properties may be of use in the development of prevention and treatment strategies for SDFT rupture.