Etiology, diagnosis and treatment of tendonitis: an analysis of the literature. Med. Sci. Sports Exerc., Vol. 30, No. 8, pp. 1183-1190, 1998. Tendonitis is a common diagnosis in sports medicine. The traditional view of tendonitis is a tendon injury resulting from repetitive mechanical load with a subsequent inflammatory response. The English literature from 1966 to the present on the etiology, diagnosis, and treatment of tendonitis was evaluated. There is some scientific support in the literature for the diagnosis of tenosynovitis and tendinosis as a pathologic entity. Actual inflammation of tendon tissue consistent with tendonitis has not been seen clearly in patho-anatomic studies. Conclusive evidence confirming that repetitive mechanical load is a major etiologic factor could not be found. Similarly, strength deficits, inflexibility, and improper equipment have not been studied in a controlled prospective manner. Other factors such as age and tendon vascularity have been consistently correlated with these injuries although their overall importance remains difficult to assess. There are no controlled studies on treatment through physical therapy aimed at flexibility and/or strengthening. Treatment with anti-inflammatory drugs has been studied extensively. However, only nine of 32 studies are prospective and placebo controlled. Some pain relief was found in five of the nine controlled studies, but healing of the tendon problem was not studied in these short follow-up studies. Twenty-three studies on steroid injections were found. Eight were prospective and placebo controlled studies, with three showing beneficial effects of the injection at follow-up. It was concluded that much of the pathology and etiology of tendonitis remains unclear. The possibility must be considered that current treatment methods may not significantly affect the natural history.