Specialization of tendon mechanical properties results from interfascicular differences

Area of Science:

• Biomechanics
• Tendon mechanics
• Equine sports medicine

Background:

• Tendons transmit muscle forces to bone, with some storing and returning energy.
• Energy-storing tendons (e.g., SDFT) require greater extensibility than positional tendons (e.g., CDET).
• The relationship between matrix organization and distinct mechanical properties in tendons is not fully understood.

Purpose of the Study:

• To investigate how matrix organization influences the mechanical properties of energy-storing (SDFT) and positional (CDET) tendons.
• To compare the properties of whole tendons, fascicles, and the fascicular interface in SDFT and CDET.
• To elucidate the mechanisms behind the differential mechanical behavior of these functionally distinct tendons.

Main Methods:

• Comparative analysis of whole tendons, fascicles, and fascicular interfaces from equine SDFT and CDET.
• In vitro mechanical testing to determine stress, strain, modulus, and failure properties.
• Assessment of fascicle sliding at the interfascicular level under physiological loads.

Main Results:

• Tendon fascicles exhibited lower failure stress and strain compared to whole tendons.
• The SDFT demonstrated higher overall extensibility than the CDET.
• Lower stiffness at the SDFT fascicular interface facilitated greater fascicle sliding, explaining differences in tendon versus fascicle failure strain.

Conclusions:

• Fascicle sliding at the interfascicular interface is a key mechanism enabling high strain in energy-storing tendons like the SDFT.
• This sliding mechanism protects fascicles from damage during high-demand activities.
• Understanding these differences is crucial for equine tendon injury prevention and treatment.