Tendon injuries: Basic science and new repair proposals

Abstract

Tendons connect muscles to bones, ensuring joint movement. With advanced age, tendons become more prone to degeneration followed by injuries. Tendon repair often requires lengthy periods of rehabilitation, especially in elderly patients. Existing medical and surgical treatments often fail to regain full tendon function.The development of novel treatment methods has been hampered due to limited understanding of basic tendon biology. Recently, it was discovered that tendons, similar to other mesenchymal tissues, contain tendon stem/progenitor cells (TSPCs) which possess the common stem cell properties.The current strategies for enhancing tendon repair consist mainly of applying stem cells, growth factors, natural and artificial biomaterials alone or in combination. In this review, we summarise the basic biology of tendon tissues and provide an update on the latest repair proposals for tendon tears. Cite this article: EFORT Open Rev 2017;2:332-342. DOI: 10.1302/2058-5241.2.160075.

Keywords: biomaterials; cell-based therapy; growth factors; mesenchymal stem cells; tendon repair; tendon stem/progenitor cells.

Fig. 1

Simplified cartoon model of Achilles tendon anatomical structure. Paratenon sheet surrounds the whole tendon, while endotenon sheets surround individual tendon fascicles. Scarce blood vessels and nerve fibres (not shown) are located within the sheets. Each fascicle is composed of collagen fibres with variable diameter size situated in proteoglycan-rich matrix, while each collagen fibre is composed of multiple collagen type I fibrils. In between fibres, tenocytes (terminally differentiated cells) are found. Tendon stem cells are suggested to be located in the tendon sheets, near the blood vessels or within the intra-fascicular matrix. Based on Docheva et al.