Postnatal Development of the Functional Specialization of the Equine Superficial Digital Flexor Tendon

Introduction: The superficial digital flexor tendon (SDFT) is adapted to its function of both withstanding high loads, as well as providing a structure, which is fatigue-resistant, elastic and stores energy. We have shown previously that many of the unique SDFT properties are derived from a specialized compartment of tendon, known as the inter-fascicular matrix (IFM). We were interested in understanding how the SDFT develops its unique structure from birth to the end-of-development. Understanding this process may lead to development of methods which could be used to optimize tendon structure for future resilience to athletic use.

Materials and Methods: We undertook histology/immunohistochemistry and proteomics on dissected fascicular matrix (FM) and IFM, and hierarchical biomechanical testing of fascicles and the IFM in tendons collected from horses from 0 to 24 months.

Results: The FM shows little adaptation post-natally; its proteome showed little alteration through development, and little alteration in biomechanical properties other than a slight increase in viscoelastic properties at the end of growth. In contrast the IFM demonstrates adaptation of its proteome, structure and biomechanical properties throughout the whole period of development.

Discussion/Conclusion: We demonstrate that the SDFT develops its unique functional properties throughout the whole period of growth (0–2 years). While there is some adaptation of this tendon immediately after birth, most of the specific specialization of this tendon occurs at the yearling stage and continues on until the end of growth. To optimize tendon development any interventions will have to be targeted at the full period of development, not just the immediate postnatal period.

Acknowledgement: Funding: HBLB.