Shear load transfer in high and low stress tendons

Area of Science:

• Biomechanics
• Tendon Mechanics
• Material Science

Background:

• Tendons transmit muscle loads to bone, crucial for joint movement and stability.
• Tendon structure is anisotropic and hierarchical, typically loaded along fiber direction.
• Damage or altered joint mechanics can induce inter-fiber shear, affecting load distribution.

Purpose of the Study:

• Investigate shear stress redistribution of axial loads in tendons with different microstructures.
• Compare load redistribution in rat tail tendons (linear microstructure) and porcine flexor tendons (helical microstructure).
• Quantify the impact of varying laceration depths on tendon mechanical properties.

Main Methods:

• Created controlled lacerations (20-60% width) in rat tail and porcine flexor tendons to induce shear.
• Analyzed fascicular orientation using polarized light microscopy.
• Measured changes in stress, elastic stress, and modulus post-laceration.

Main Results:

• Both tendon types retained approximately 20% of pre-laceration stress after 60% width lacerations.
• Structural parameters decreased linearly with increasing laceration depth for both tendon types.
• Rat tail tendons exhibited a more rapid decline in mechanical properties and a less organized fascicular structure.

Conclusions:

• Shear stress transfer plays a more significant role in tendon strength and stiffness than previously understood.
• Tendon microstructure influences its ability to redistribute loads via shear.
• Positional tendons with linear microstructures may be less efficient at load redistribution through shear compared to helical structures.