Etiology and pathophysiology of chronic tendon disorders in sports.

In sports medicine, a chronic overuse injury is defined as a long-standing or recurring orthopedic problem and pain in the musculoskeletal system, which started during exertion due to repetitive tissue microtrauma (1). Repetitive microtrauma, which is basically repeated exposure of the musculoskeletal tissue to low-magnitude forces, results in injury at the microscopic level, and no single acute trauma is normally involved in the pathogenesis of an overuse injury. In chronic tendon disorders, 'overuse' implies that the tendon has been strained repeatedly to 4-8% strain until unable to endure further tension, whereupon injury occurs (2). The structure of the tendon is disrupted micro- or macroscopically by this repetitive strain, i.e. collagen fibrers begin to slide past one another, causing break-age of their cross-linked structure, and denaturate; inflammation, edema and pain result. Thus, tendinitis, peritendinitis, tenosynovitis, insertion tendinitis, tendinous bursitis or apophysitis is the earliest clinically recognizable manifestation of overuse tendon injury (3).