The three common terms used to refer to tendon injuries or overuse injuries are extremely confusing. Much of the time, the difference between these entities is not apparent at all and they seem to be used interchangeably. Since there also exists disagreement among practitioners as to what internal changes actually constitute what condition, the layperson is left even more befuddled. Both tendonitis and tendonosis are much more common terms than tendonopathy.
-Itis Medical Term
The most common of the three terms is tendonitis. The suffix “-itis” means inflammation. So the term tendonitis means inflammation of the tendon and of the tendon-muscle attachments. This term is used to refer to most tendon injuries even though such injuries may feature degenerative changes with little evidence of inflammatory cells. In fact, little evidence of an inflammatory process has been found in experimental models of tendonitis using chronically overloaded animal limb muscles.
Otis Medical Term
An alternative model is tendonosis. The suffix “-osis” refers to a diseased or abnormal state. Therefore, the term tendonosis would refer to a tendon being abnormal or diseased. This condition is described as degenerative changes brought on by acute trauma or several strains to the tissue that exceed the ability of the tissue to heal, thus resulting in repetitive injury and the deposition of scar tissue.
The difference between tendonosis and tendonitis is that tendonosis features tendon damage at the cellular level which does not show inflammation and is degenerative in nature. Many conditions referred to as tendonitis may more accurately be called tendonosis.
It may well be that there is no difference between overuse injuries commonly called tendonitis versus those called tendonosis. When the tissues of “tendonitis” are looked at under a microscope there seems to be no neutrophil reaction, which would indicate an acute inflammatory response, but rather the tissue changes seem to be consistent with chronic degenerative changes, lending credence to the tendonosis theory.
Since corticosteroid injections sometimes help conditions without apparent inflammation, even more questions emerge as to the role of cytokines in these conditions and the merit of the two classifications.
-Pathy Medical Term
The suffix “-pathy” comes from the Greek word pathos meaning suffering or disease. Tendonopathy, therefore, is a catchall term meaning “disease of the tendon” and does not try to differentiate the role of inflammation versus other changes. It may be that tendonopathy is a better term in general for these conditions. In fact, some recent studies have considered whether “tendonitis” is but a myth due to the aforementioned absence of inflammatory cells in histological examination.
Some experts have therefore decided that “tendonosis” is a better term whereas by others “tendonopathy” is considered to be a better choice. Clearly, acute traumatic injuries are different than chronic overuse injuries that are the result of accumulated micro-trauma, and this guides the treatment of such injuries.
However, for the layperson, there is no need to be confused by these terms. It probably does not matter whether you call your condition tendonitis or tendonosis, as long as your health professional is not confused!
Other terms used to describe overuse injuries include myositis, myotendonitis, and tenosynovitis.
Note to the reader: Even more confusion may be generated by some frequently used alternative spellings. Tendonosis is sometimes spelled as tendinosis and tendonopathy as tendinopathy. Since there is no such thing as a tendin this article avoids using these misspellings, except in the title, as tendinopathy is such a widespread usage I used it to help people find this article in searches.