The intrinsic pathogenetic mechanisms of tendinopathies are largely unknown and whether inflammation or degeneration has the prominent role is still a matter of debate. Assuming that there is a continuum from physiology to pathology, overuse may be considered as the initial disease factor; in this context, microruptures of tendon fibers occur and several molecules are expressed, some of which promote the healing process, while others, including inflammatory cytokines, act as disease mediators. Neural in-growth that accompanies the neovessels explains the occurrence of pain and triggers neurogenic-mediated inflammation. It is conceivable that inflammation and degeneration are not mutually exclusive, but work together in the pathogenesis of tendinopathies.

This article reviews the pathogenetic role of metabolic disorders, which are of paramount relevance to the progression of tendon damage. In diabetes, the prevalence of rheumatological diseases is high, mainly because of the deleterious effects of advanced glycation end products that deteriorate the biological and mechanical functions of tendons and ligaments. In heterozygous familial hypercholesterolaemia, most patients develop Achilles xanthomatosis, a marker of high risk for cardiovascular disease caused by cholesterol deposition in the tendons. Tendon degeneration has also been observed in non-familial hypercholesterolaemia. Monosodium urate crystal deposition in soft tissues is a hallmark of chronic gouty arthritis. In this group of diseases, the mobilization of cholesterol and uric acid crystals is presumably followed by low-grade inflammation, which is responsible for tendon degeneration. Adiposity may contribute to tendon disorders via two different mechanisms: increased weight on the load-bearing tendons and systemic dysmetabolic factors that trigger subclinical persistent inflammation. Finally, tendon abnormalities have been observed in some rare congenital metabolism disorders such as alkaptonuria.

The prevalence of rotator cuff tears increases with age and several studies have shown that diabetes is associated with symptomatic shoulder pathologies. Aim of our research was to evaluate the prevalence of shoulder lesions in a population of asymptomatic elderly subjects, normal and with non insulin - dependent diabetes mellitus.

Cigarette smoking has deleterious effects on the musculo-skeletal system. The loss of bone mineral content and increased incidence of fractures are the best known negative consequences. The pathogenesis is complex, due to direct toxic effects on osteoblasts/osteoclasts activity of nicotine, and indirect actions on sex and adrenocortical hormones, vitamin D, intestinal calcium absorption, vessels and oxygen supply. Smoking may favour the onset or aggravate the progression of rheumatoid arthritis and back pain. Negative influences have been observed on muscle and on tendons. Moreover, smoking habit is associated to a number of short term post-operative complications and higher resource consumption. Smoking cessation is highly advisable with positive effects on the bone metabolism on the long term. More positive and immediate results can be obtained in patients submitted to orthopedic surgery: the healing process is improved, the frequency of complications is reduced, and the length of hospital stay is shortened.

Limited joint mobility is frequently observed in elderly people and in patients suffering from diabetes, who represent a growing segment of the population of western countries. Our review wishes to offer the “state of art” about this interesting topic, which may have important clinical implications, leading to impairment of both basic and instrumental activities of daily living. The main causes of a reduced range of motion are degenerative joint diseases and increased stiffness of collagen tissue. The main biochemical abnormality, common to aging and diabetes, is the non-enzymatic glycosilation of collagen, with advanced glycation end product (AGE) formation, which in turn leads to an increase of collagen cross-links. The most extensive accumulation of AGEs occurs in tissues that contain proteins with low turnover, such as the collagen in the extracellular matrix of articular capsule, ligaments and muscle-tendon units. The increase in collagen cross-linking alters the mechanical properties of these tissues with a decrease in elasticity and tensile strength, and an increase in mechanical stiffness. Besides this, AGEs react with specific cell surface receptors (RAGEs). The engagement of the ligand by RAGEs triggers cell-specific signalling, resulting in enhanced generation of reactive oxygen species and sustained up-regulation of pro-inflammatory mediators and adhesion molecules. An appropriate control of the glucose levels and a diet rich in antioxidant agents are recommended in patients with diabetes. Stretching and strengthening programmes are widely used, in order to prevent and to reduce joint stiffness, but the improvements with physiotherapy are little and short-lasting. Several drugs, which can interfere with AGE formation and removal, or with the cellular effects of AGEs, are under study (among them pyridoxamine, an active form of Vitamin B6, AGE-breaker compounds, glucosamine, rutin and derivatives, soluble RAGE isoforms, and statins). In experimental animal models, these drugs are effective in reducing diabetic complications due to AGE formation; however, further study is necessary before their extensive use in the clinical setting.