The Basic Science of Tendinopathy

Abstract

Tendinopathy is a common clinical problem with athletes and in many occupational settings. Tendinopathy can occur in any tendon, often near its insertion or enthesis where there is an area of stress concentration, and is directly related to the volume of repetitive load to which the tendon is exposed. Recent studies indicate tendinopathy is more likely to occur in situations that increase the ''dose'' of load to the tendon enthesis -including increased activity, weight, advancing age, and genetic factors. The cells in tendinopathic tendon are rounder, more numerous, and show evidence of oxidative damage and more apoptosis. These cells also produce a matrix that is thicker and weaker with more water, more immature and cartilage-like matrix proteins, and less organization. There is now evidence of a population of regenerating stem cells within tendon. These studies suggest prevention of tendinopathy should be directed at reducing the volume of repetitive loads to below that which induces oxidative-induced apoptosis and cartilage-like genes. The management strategies might involve agents or cells that induce tendon stem cell proliferation, repair and restoration of matrix integrity.

The Achilles Tendinopathy: Pathogenesis Review

“…Mechanical overload, hypoxia, oxidative stress (caused by free radicals) are all factors thought to determine dysregulated apoptosis, probably a cause of tendinopathy [117] . The caspase and nitric oxide (NO) pathways play a role in tendon apoptosis; the expression of caspase-8 and the enzyme that catalyses the formation NO, named nitric oxide synthase (NOS), were found to be elevated in tendinopathy [118,119] .…”

Tendon — function-related structure, simple healing process and mysterious ageing

“…Macroscopically a healthy tendon appears as fibro-elastic, solid structure in brilliant, white color [62]. At microscopic and molecular levels they are characterized by a hierarchical structure, which guarantees high mechanical strength, endurance to repetitive loads and minimizes the risk of failures and injuries [4].As all connective tissue structures tendons are composed of fibers (mostly type I collagen), extracellular matrix (ECM; mostly proteoglycans, glycoproteins) and cells (predominantly tenocytes); despite their solid structure, tendons are highly hydrated and contain approximately 70% of water (mostly associated with proteoglycans).…”

“…The ECM is a structure, which creates a kind of scaffolding for cells, vessels and nerves and is composed of collagen molecules, proteoglycans, glycoproteins and other small molecules [62]. The main component of ECM is type I collagen, which constitutes approximately 95% of total collagen content in tendon tissue [62].…”

“…The main component of ECM is type I collagen, which constitutes approximately 95% of total collagen content in tendon tissue [62]. Among other collagen types found in tendons the most important is type III collagen, which is characterized by smaller and weaker fibers with reduced resistance and is typically found in endotenon and epitenon sheets [8].…”

“…Another type of molecules found in ECM are proteoglycans -a group of different substances, represented by: aggrecan, biglycan, decorin, perlecan, agrin, laminin, versican, lumican, fibromodulin [32]. They are responsible for visco-elastic properties of the tendon and provide protection against compressive forces [62]. They also help retaining water molecules within the tendon, play a lubricating role and contribute to collagen fibrils fusion [32,50].…”