Structure‐function relationships in tendons: a review

Abstract

The purpose of the current review is to highlight the structure-function relationship of tendons and related structures to provide an overview for readers whose interest in tendons needs to be underpinned by anatomy. Because of the availability of several recent reviews on tendon development and entheses, the focus of the current work is primarily directed towards what can best be described as the 'tendon proper' or the 'mid-substance' of tendons. The review covers all levels of tendon structure from the molecular to the gross and deals both with the extracellular matrix and with tendon cells. The latter are often called 'tenocytes' and are increasingly recognized as a defined cell population that is functionally and phenotypically distinct from other fibroblast-like cells. This is illustrated by their response to different types of mechanical stress. However, it is not only tendon cells, but tendons as a whole that exhibit distinct structure-function relationships geared to the changing mechanical stresses to which they are subject. This aspect of tendon biology is considered in some detail. Attention is briefly directed to the blood and nerve supply of tendons, for this is an important issue that relates to the intrinsic healing capacity of tendons. Structures closely related to tendons (joint capsules, tendon sheaths, pulleys, retinacula, fat pads and bursae) are also covered and the concept of a 'supertendon' is introduced to describe a collection of tendons in which the function of the whole complex exceeds that of its individual members. Finally, attention is drawn to the important relationship between tendons and fascia, highlighted by Wood Jones in his concept of an 'ectoskeleton' over half a century ago -work that is often forgotten today.

The past, present and future in scaffold-based tendon treatments

“…Human and equine tendons are comprised of various cell populations (Figure 1 and Table 2), with similar characteristics between species [58,59]. Around 90-95% of the cells present in tendon are elongated specialised fibroblasts, termed tenocytes (TC), and their precursor cells, termed tenoblasts.…”

“…Similarly, NSAIDs have a beneficial effect on injured tendons, should they injected soon after the injury occurs (a few days); however, patient response to the treatment varies widely, side effects associated with prolonged use and their detrimental effect on cell proliferation and PG synthesis further compromise their use [143][144][145]. The use of glucocorticoids, as inflammation suppressive drugs, has also been advocated in tendon field [59],…”

Restricted differentiation potential of progenitor cell populations obtained from the equine superficial digital flexor tendon (SDFT)

“…In the equine SDFT, peritenon cells displayed decreased clonogenicity and both osteogenic and adipogenic differentiation, but were reported to have increased proliferation and increased expression of progenitor cell markers 15. Tendons are relatively poorly vascularized16 and tendon cells reside within a hypoxic environment. Culture of TPSCs in 2% oxygen has been reported to increase proliferation but to reduce multipotency,17, 18 whereas 5% oxygen reportedly both increases proliferation and maintains stemness 19…”

A MINI REVIEW ON THE BASIC KNOWLEDGE ON TENDON: REVISITING THE NORMAL & INJURED TENDON

“…Normal tendon ECM is composed largely of collagen (predominantly type-I collagen, COL-I 1 ), which provides structural integrity and mechanical strength (13). A small amount of ground substances (Table 1) is not only important in fibrillogenesis but also provides tendon its high resistance behaviour to compressive and tensile forces (14).…”