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

Abstract

While it is known that musculotendon units adapt to their load environments, there is only a limited understanding of tendon adaptation in vivo. Here we develop a computational model of tendon remodeling based on the premise that mechanical damage and tenocyte-mediated tendon damage and repair processes modify the distribution of its collagen fiber lengths. We explain how these processes enable the tendon to geometrically adapt to its load conditions. Based on known biological processes, mechanical and strain-dependent proteolytic fiber damage are incorporated into our tendon model. Using a stochastic model of fiber repair, it is assumed that mechanically damaged fibers are repaired longer, whereas proteolytically damaged fibers are repaired shorter, relative to their pre-damage length. To study adaptation of tendon properties to applied load, our model musculotendon unit is a simplified three-component Hill-type model of the human Achilles-soleus unit. Our model results demonstrate that the geometric equilibrium state of the Achilles tendon can coincide with minimization of the total metabolic cost of muscle activation. The proposed tendon model independently predicts rates of collagen fiber turnover that are in general agreement with in vivo experimental measurements. While the computational model here only represents a first step in a new approach to understanding the complex process of tendon remodeling in vivo, given these findings, it appears likely that the proposed framework may itself provide a useful theoretical foundation for developing valuable qualitative and quantitative insights into tendon physiology and pathology.

Finding the sweet spot via personalised Achilles tendon training: the future is within reach

“…This cascade is affected by cell arrangement, shape and attachment to the ECM, as well as the local biochemical environment 9. Computational model studies have further demonstrated that tendon strain and ECM damage can predict protein expression9 and explain tendon adaptation 10. Therefore, if it were possible to design personalised exercise programmes to strain tendon within the ‘sweet spot’, taking into account the current structure, material properties and biochemical environment, then clinical efficacy of exercise-based rehabilitation should improve.…”

A Finite Element Model for Trigger Finger

“…The cross-sectional area of a flexor tendon mid-section can range from 8.36 to 14.44 mm 2 [51,52] for an index finger. For this simplified model, the assumption made was that the FDP, FDS and EDC all have an initial average circular cross-sectional area, A, taken from the literature [53] (Table 7). Assuming homogenous material properties, uniform stiffness k for collagen can also be adopted along the tendon length [53].…”

Targeted Achilles Tendon Training and Rehabilitation Using Personalized and Real-Time Multiscale Models of the Neuromusculoskeletal System

“…A systematic review of human tendon adaptation in response to mechanical loading further concluded that, on the basis of 27 included studies, while tendons are responsive to a range of loading conditions, loading magnitude (and hence strain), in particular, plays a key role in tendon adaptation (Bohm et al, 2015). While there remains much to learn about the specific loading conditions (i.e., strain magnitude, strain duration, strain frequency, and strain rate) that maximize tendon adaptation and the mechanobiological pathway involved (Smith et al, 2013;Young et al, 2016), tendon strain magnitude appears to play a fundamental role.…”