Adaptive Remodeling of Achilles Tendon: A Multi-scale Computational Model

Area of Science:

• Biomechanics
• Computational Biology
• Tendon Physiology

Background:

• Musculotendon units adapt to load, but in vivo tendon adaptation mechanisms are poorly understood.
• Tendon remodeling involves complex interactions between mechanical damage, cellular repair, and collagen fiber organization.

Purpose of the Study:

• To develop a computational model of tendon remodeling in vivo.
• To investigate how mechanical damage and tenocyte-mediated repair influence collagen fiber length distribution and tendon geometry.
• To explore the relationship between tendon adaptation and metabolic cost during muscle activation.

Main Methods:

• Developed a computational model incorporating mechanical and strain-dependent proteolytic fiber damage.
• Modeled tendon repair as a stochastic process where damaged fibers are repaired to different lengths.
• Utilized a simplified three-component Hill-type model of the human Achilles-soleus musculotendon unit.

Main Results:

• The model demonstrates how damage and repair processes enable geometric adaptation of tendons to load conditions.
• Achilles tendon geometric equilibrium was found to coincide with minimized total metabolic cost of muscle activation.
• Predicted collagen fiber turnover rates align with in vivo experimental measurements.

Conclusions:

• The proposed computational framework offers a theoretical foundation for understanding in vivo tendon remodeling.
• Findings provide insights into tendon physiology and pathology, particularly concerning adaptation to mechanical loads.
• This model represents a significant step towards a comprehensive understanding of complex tendon adaptation processes.