Tendon crimps and peritendinous tissues responding to tensional forces

Area of Science:

• Biomechanics
• Connective Tissue Research
• Musculoskeletal System

Background:

• Tendons transmit muscle-generated forces to bones, enabling joint movement.
• Tendon collagen exhibits a complex hierarchical structure, with fibrils forming fibers and fascicles.
• The role of tendon sheaths in force absorption and transmission during muscle contraction is not fully understood.

Purpose of the Study:

• To investigate the structural differences between tendon collagen fibrils and tendon sheaths.
• To determine the role of fibrillar crimps in tendon function, particularly shock absorption.

Main Methods:

• In vivo passive stretching of rat Achilles tendons.
• Microscopic analysis using polarized light microscopy (PLM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).

Main Results:

• Tendon collagen fibers displayed a periodic crimp pattern, with heterogeneous fibrils undergoing localized modifications termed 'fibrillar crimps'.
• Tendon sheaths showed uniform fibrils with a wavy course but lacked the ultrastructural aspects of fibrillar crimps.
• Fibrillar crimps remained observable in passively stretched tendons, suggesting their role in shock absorption.

Conclusions:

• Fibrillar crimps are likely the primary structural component responsible for tendon crimp and act as shock absorbers during stretching and muscle contraction.
• Tendon sheaths can stretch but are not actively involved in shock absorption due to their different fibril structure.
• Differences in fibril arrangement and molecular structure account for the distinct functional roles of tendons and their sheaths.