Shear loads induce cellular damage in tendon fascicles

Abstract

Tendon is vital to musculoskeletal function, transferring loads from muscle to bone for joint motion and stability. It is an anisotropic, highly organized, fibrous structure containing primarily type I collagen in addition to tenocytes and other extracellular matrix components contributing to maintenance and function. Tendon is generally loaded via normal stress in a longitudinal direction. However, certain situations, including fiber breakage, enzymatic remodeling, or tendon pathology may introduce various degrees of other loading modalities, such as shear-lag at the fiber level, potentially affecting cellular response and subsequent function. Fascicles from rat tail tendon were dissected and placed in one of three paired groups: intact, single laceration, or double laceration. Each pair had a mechanically tested and control specimen. Single laceration fascicles contained one transverse laceration to mimic a partial tear. Double laceration fascicles had overlapping, longitudinally separated lacerations on opposite sides to cause intra-fascicular shear transfer to be the primary mechanism of loading. Elastic properties of the fascicle, e.g. peak load, steady state load, and stiffness, decreased from intact to single laceration to double laceration groups. Surprisingly, 45% of the intact strength was maintained when shear was the primary internal load transfer mechanism. Cellular viability decreased after mechanical testing in both laceration groups; cell death appeared primarily in a longitudinal plane where high shear load transfer occurred. This cell death extended far from the injury site and may further compromise an already damaged tendon via enzymatic factors and subsequent remodeling associated with cell necrosis.

Biplanar ultrasound investigation of in vivo Achilles tendon displacement non-uniformity

“…Although rat Achilles tendon may not be functionally representative of human Achilles tendon, it nevertheless serves as a model for a tendon in which the distal tendon is a union of tendon fascicles arising from muscles with different anatomical and functional properties similar to human Achilles tendon. Such mechanisms of lateral force transmission could be important for protecting the Achilles tendon from excessive shearing that may lead to cellular damage at the interfaces between tendon fascicles . In the current study, it is also possible that changes in muscle‐tendon unit passive tension due to alterations in knee joint angle contributed to the observed results.…”

Anin vitroscratch tendon tissue injury model: effects of high frequency low magnitude loading

“…We consider our current (newly developed) technique an advancement to the above protocol since introduction of mechanical damage by fatigue cyclic loading may likely produce spontaneous, catastrophic and uncontrolled damage in isolated tendon fascicles.More recently, Kondratko-Mittnacht et al 2015 produced transverse laceration damage in RTTFs by using a razor blade to penetrate 50-70% of an individual fascicle width[14]. We produced aconsistent scratch length of 0.77±0.06cm in individual rat tail tendon fascicles, in spite of an initial target scratch length of 1cm.…”

“…A c c e p t e d M a n u s c r i p t However the mechanism used for mechanical treatment of each RTTFs (cyclic loading) in the study was short lived (less than 1 minute in total), did not include a culture system, and thus did not allow for factors associated with cellular response and tissue remodelling in damaged tendons. Also, incorrect handling of lacerated tendon fascicles under non-aseptic conditions may have led to the drop in viability after the mechanical treatment period of approximately 20 seconds [14].…”

“…More recently, Kondratko-Mittnacht, J., 2015 became the first to produce lacerations in the transverse direction of individual rat tail tendon fascicles in vitro by using a razor blade to penetrate 50-70% of the fascicle width to achieve clinically relevant damage in tendon tissue [14]. However, this damage model is not used as part of a culture system, thus there are no indications about its usefulness in studying mid-long term tendon mechanobiological effects.…”

The Role of Detraining in Tendon Mechanobiology

“…This mechanosensitive tissue shows detailed mechanical properties that allow it to adapt and respond to loading transmitted by muscles (Fang and Lake, 2015 ). This load transfer provide the principal mechanical stimulus for tendon cells (Kondratko-Mittnacht et al, 2015 ). These tensile loads are diverted to tendon cells through different matrix compartments and components.…”