Tendon Biomechanics and Crimp Properties Following Fatigue Loading Are Influenced by Tendon Type and Age in Mice

Abstract

In tendon, type‐I collagen assembles together into fibrils, fibers, and fascicles that exhibit a wavy or crimped pattern that uncrimps with applied tensile loading. This structural property has been observed across multiple tendons throughout aging and may play an important role in tendon viscoelasticity, response to fatigue loading, healing, and development. Previous work has shown that crimp is permanently altered with the application of fatigue loading. This opens the possibility of evaluating tendon crimp as a clinical surrogate of tissue damage. The purpose of this study was to determine how fatigue loading in tendon affects crimp and mechanical properties throughout aging and between tendon types. Mouse patellar tendons (PT) and flexor digitorum longus (FDL) tendons were fatigue loaded while an integrated plane polariscope simultaneously assessed crimp properties at P150 and P570 days of age to model mature and aged tendon phenotypes (N = 10–11/group). Tendon type, fatigue loading, and aging were found to differentially affect tendon mechanical and crimp properties. FDL tendons had higher modulus and hysteresis, whereas the PT showed more laxity and toe region strain throughout aging. Crimp frequency was consistently higher in FDL compared with PT throughout fatigue loading, whereas the crimp amplitude was cycle dependent. This differential response based on tendon type and age further suggests that the FDL and the PT respond differently to fatigue loading and that this response is age‐dependent. Together, our findings suggest that the mechanical and structural effects of fatigue loading are specific to tendon type and age in mice. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:36–42, 2020

Impact of Uniaxial Stretching on Both Gliding and Traction Areas of Tendon Explants in a Novel Bioreactor

“…Comparing FLD and patellar tendon in mice, Zuskov et al were recently able to make the same point [24].…”

“…The mechanical characteristics of the tendon are relatively uniform across a range of vertebrate animals, such as rabbit or rat [22,23], and therefore animal models are often used in the field of tendon pathology and repair. The choice of animal depends on the modalities of the mechanical loading of the tendon [24]. Presently, based on the knowledge of tendon fatigue leading to tendinopathy, and potentially to tendon rupture, rat and mice tendons were used in the development of an in vivo fatigue model [25].…”

Viscoelastic characteristics of the canine cranial cruciate ligament complex at slow strain rates

“…The phenomenon of viscoelastic characteristics including strain rate dependency, hysteresis, creep and stress relaxation has been observed consistently in soft biological tissues such as the sclera (Elsheikh et al, 2010;Geraghty et al, 2020), cornea (Elsheikh et al, 2011;Kazaili et al, 2019), and tendon (Robinson et al, 2004;Zuskov et al, 2020). Similarly, ligaments inherit non-linear viscoelastic characteristics exhibiting both elastic and viscous behaviour, hence they are history-and time-dependent (Bonner et al, 2015;Fung, 1993;Ristaniemi et al, 2018).…”

Induced Knockdown of Decorin, Alone and in Tandem With Biglycan Knockdown, Directly Increases Aged Murine Patellar Tendon Viscoelastic Properties

“…The cause of this age-associated injury risk remains unknown and is not directly explained by changes in tendon mechanical properties. While some animal studies report decreases in tendon mechanical properties with age [4][5][6][7], other studies report moderate or no differences in mechanical properties across ages [8][9][10]. Age-related mechanical changes (or lack thereof) may be tissue-specific, but dynamic properties, especially dynamic modulus, are affected by age when measured [4,7].…”