The pathologic label tendinosis is used to describe the disorganized impaired healing response in tendinopathy. Despite that, most clinicians still use the term tendonitis or tendinitis, thus implying that the fundamental problem is inflammatory. We advocate the use of the term tendinopathy as a generic descriptor of the clinical conditions in and around tendons arising from overuse, and suggest that the terms tendinosis, tendonitis and tendinitis only be used after histopathological examination.24
Histologically, Achilles tendinopathy is characterized by an absence of inflammatory cells and a poor healing response. Other changes include: noninflammatory intratendinous collagen degeneration, fiber disorientation and thinning, hypercellularity, scattered vascular ingrowth, and increased interfibrillar glycosaminogly-cans.4,8,25 Frank inflammatory lesions and granulation tissue are mostly associated with tendon ruptures.26
Various types of so-called degeneration may be seen in tendons, but in the Achilles tendon "mucoid" or "lipoid" degeneration is usually seen.26 In mucoid degeneration, light microscopy reveals large mucoid patches and vacuoles between fibers. In lipoid degeneration, abnormal intraten-dinous accumulation of lipid occurs, with disruption of collagen fiber structure.25
Paratendinopathy may occur alone or in combination with degeneration of the tendon body.27 Histologically, mucoid degeneration, fibrosis, and vascular proliferation with a slight inflammatory infiltrate have been reported.5'28'29 Clinically, edema and hyperemia of the paratenon are seen. A fibrinous exudate accumulates within the tendon sheath, and crepitus may be felt on clinical examination.17
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