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Growth factors may be useful in tendon healing, possibly introduced using gene therapy
Tendon disorders are a major problem in sports and occupational medicine. Tendons have the highest tensile strength of all connective tissue because of a high proportion of collagen in the fibres and their closely packed parallel arrangement in the direction of force. The individual collagen fibrils are arranged into fascicles which contain blood vessels and nerve fibres. Specialised fibroblasts, tenocytes, lie within these fascicles and exhibit high structural organisation.1 Histologically, they appear as star shaped cells in cross sections. In longitudinal sections, they are arranged in rows following the direction of the tendon fibres. This specialised arrangement is related to their function, as tenocytes synthesise both fibrillar and non-fibrillar components of the extracellular matrix, and are able to reabsorb collagen fibrils.2 The fascicles themselves are enclosed by epitenon. This is surrounded by the paratenon, and the potential space between them is filled by a thin, lubricating film of fluid which allows gliding of the tendon during motion.
BIOLOGY OF TENDON HEALING
Tendon healing is classically considered to occur through extrinsic and intrinsic healing. The intrinsic model produces obliteration of the tendon and its tendon sheath. Healing of the defect involves an exudative and a formative phase which, on the whole, are very similar to those associated with wound healing.3 Extrinsic healing occurs through the chemotaxis of the specialised fibroblasts into the defect from the ends of the tendon sheath.4 The process can be divided into three phases: inflammation, repair, and organisation or remodelling. In the inflammatory phase, occurring three to seven days after the injury, cells migrate from the extrinsic peritendinous tissue such as the tendon sheath, periosteum, subcutaneous tissue, and fascicles, as well as from the epitenon and endotenon.5 Initially, the …