Objectives-To analyse the glycosaminoglycans of the adult human rotator cuff tendon matrix, to characterise changes in the glycosaminoglycan composition with age and in chronic rotator cuff tendinitis. Methods-Rotator cuff (supraspinatus) tendons (n = 84) and common biceps tendons (n = 26) were obtained from cadavers with no history of tendon pathology (age range 11-95 years). Biopsies of rotator cuff tendons (supraspinatus and subscapularis tendons, n = 53) were Conclusions-The normal supraspinatus tendon has the proteoglycan/glycosaminoglycan of tendon fibrocartilage, which it is suggested is an adaptation to mechanical forces (tension, compression and shear) which act on the rotator cuff tendons in the shoulder, although other factors such as reduced vascularity, low oxygen tension and the influence of local growth factors may also be important. This functional adaptation may have important consequences for the structural strength of the supraspinatus tendon and to influence the ability of the tendon to repair after injury. The glycosaminoglycan composition of tendon specimens from patients with chronic tendinitis is consistent with acute inflammation and new matrix proteoglycan synthesis, even in relatively old tendon specimens and after at least one injection of corticosteroid. (Ann Rheum Dis 1994; 53: 367-376) Chronic shoulder pain is a common and disabling condition that is often seen in rheumatological practice and prevalent in the elderly community.1 1 Relatively little is known about the underlying pathology, as surgical biopsies of human tendons are rarely obtained and are not required for diagnosis. The main causes of shoulder pain are lesions of the rotator cuff tendons, most commonly the supraspinatus tendon, although the subscapularis, infraspinatus and teres minor Riley, Harrall, Constant, Chard, Cawston, Hazleman tendons may also be involved.3 The clinical description of 'tendinitis' is often used to describe painful tendon lesions, although there is little evidence for an acute inflammatory process in degenerate and spontaneously ruptured tendons. Rotator cuff tendinitis does not necessarily resolve with time and is often refractory to conservative therapies, including rest, physiotherapy and local corticosteroid injections.4 5Degeneration of the tendon matrix is generally considered to predispose to 'tendinitis' and eventual rupture, as normal tendons are immensely strong under tension.6 A variety of factors including ageing, vascular insufficiency, the anatomical shape of the acromium, impingement against osteophytes, and repetitive activities have all been implicated in the pathology of rotator cuff tendinitis.7 8 Whatever the cause, the most frequent site of all tendon lesions is the 'critical zone' in the supraspinatus tendon, approximately one centimetre from the bone insertion and a region of blood vessel anastomoses.9Although they form a minor proportion of the extracellular matrix, proteoglycans and their constituent glycosaminoglycans can influence many important physiolo...
