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Definition and classification of tendon disorders

Classification of tendon disorders

Let’s first discuss typical causes of tendon pain, regardless of the influence of fluoroquinolone antibiotics on tendon tissue. Diseases of the tendon can be roughly divided into two groups – diseases without rupture of the tendon and diseases with rupture of the tendon.

Tendon disorders without rupture

Tendon disorders without rupture are often caused by degenerative changes. Degenerative changes of tendons mostly occur in old age or with chronic overload.(1) Often hobby athletes are affected, which go beyond the limit of the tissue.

Tendon diseases without rupture also include inflammatory disease of the tendons and/or tendon sheaths.

Tendon disorders with rupture

Traumatic tendon ruptures, typically of the Achilles tendon or tendons of the shoulder joint, must be clearly distinguished from this.(1) In a tendon rupture, the tissue tears either completely or partially, which is then called a partial rupture. Typically, the cause is immediate stress well above the physiological limit.

In a rupture, the tendon is torn in two and surgical therapy is needed. In a partial rupture, the entire tendon is not torn, so there is still a functional portion of the tendon.(2)

A healthy tendon is up to two times stronger than the associated muscle, so a tendon rupture in a healthy tendon without degenerative changes is unlikely without simultaneous rupture of the muscle.(3)

Therefore, most often a degenerative tendinopathy is found histologically in a spontaneously occurring tendon rupture.(4)

Paratendinopathy: diseases of the surrounding tissue

Very often, however, pain comes from the surrounding tissue. This depends on the localization in the body and may involve tendon sheaths, bursae (bursae) or the like. In tendons with tendon sheaths, histological examination of the acute phases reveals fibrinous exudate.(5) This fibrinous exudate can sometimes be perceived as rubbing on auscultation.


Tendovaginitis refers to tendonitis, which is inflammation of the synovial layer that occurs in the tendon sheaths.(2,6)

If tendon pain is the main symptom, it is important to look for inflammation around the tendon, especially in FQAD, as in our experience it is often the case that not the tendon itself is inflamed, but rather the surrounding tissue. More on this in our article on the diagnosis of fluoroquinolone-associated tendon pain.

Confusing terminology: tendinopathy, tendinitis, or tendinosis?



The term tendinopathy refers to all diseases of the tendon.(7) The suffix -pathie means disease or illness translated from the Greek.(8)


Tendinitis is defined as acute inflammation of tendon tissue due to small microtears.3 Typically, this occurs due to acute overuse of the musculotendinous unit.(3) Previously, the term tendinitis was used to describe almost all tendon pain.2 Meanwhile, the term is most often used when swelling is present (indicating inflammation) after injury to the tendon.(9) Other typical signs of tendinitis include hyperthermia and localized tenderness. The literature shows that often the cause of tendon disease is not inflammation but degenerative changes in the tendon, so the very often diagnosed tendinitis should actually be called tendinopathy or tendinosis.(3)

A typical example of this is tennis elbow. The technical term for tennis elbow is lateral epicondylitis. The name epicondylitis suggests inflammation because of the ending. However, it is more commonly thought to be tendinosis, as no acute or chronic inflammation has been diagnosed in biopsies.(3)


The term tendinosis refers to a degenerative change in the collagen of a tendon.3 Degeneration often results from repetitive loading of the tendon with insufficient recovery time.(3) Pathologically, there is an increased presence of immature type III collagen in the tendon compared to healthy tendons with significantly more mature type I collagen. Type III collagen is always referred to as “immature collagen.” It is less stable and thinner than type I collagen. (10) Type I collagen is much more abundant in tendons than type III.(11) Type III collagen is physiologically more abundant in the dermis and blood vessels,11 and pathologically in tendinopathies as discussed above.

In tendinosis, collagen fibers are also less continuously arranged and there is increased (neo-)vascularization, i.e., formation of new blood vessels.3 These vascular structures do not result in improved blood flow and thus are not associated with healing.3 One theory is that tendon pain is caused by this neovascularization, i.e., the new formation of nonfunctional “blood vessels.“ Read about neovascularization in detail in our article on the causes of tendon pain.

So what is the significance of the distinction between tendinitis and tendinosis? 

The goal of treatment for tendinitis is to reduce inflammation, typically with NSAIDs and cortisone. In the presence of tendinosis, however, NSAIDs and cortisone are contraindicated because of an association with reduced collagen regeneration.

The distinction is also important in estimating recovery time. Tendinitis usually heals within 6 weeks whereas chronic tendinosis, in non-FQAD patients, takes 3-6 months, sometimes up to 9 months for regeneration. Tendons take 50-100 or even more days to form new collagen, depending on the source. (3,5)

Thus, it is quite apparent that even in non-fluoroquinolone-induced tendinopathy, regeneration can take a very long time.

In general, we can say that in tendinosis the goal is to stimulate collagen production and minimize the vicious cycle of repeated overuse, whereas in tendinitis the goal is to treat the inflammation and at best reduce scar tissue and adhesions.(3) Overall, both terms tendinitis and tendinosis should be used only after proper histopathologic examination.(4) However, this is rarely a clinically useful diagnosis, although the therapy between the two is very different. 

In this context, it should be noted that the division into tendinitis and tendinosis is simplified. Often, both inflammatory and degenerative aspects are present in a tendinopathy. It is therefore to be understood rather as a spectrum. Also, it is thought that in tendinosis there is a “low grade inflammation”, but this is not manifested by the classic signs of inflammation such as hyperthermia, redness or swelling.

Incidentally, it is interesting to note that tendinosis is often clinically silent, i.e., it does not cause pain.4,5 For example, in autopsies of 70-year-old individuals, tendinopathy is found in 30-50% of individuals.5 Frequently, the initial manifestation of tendinosis is a rupture. However, tendinosis may also occur together with painful paratendinopathy (that is, inflammation or damage to tissue surrounding the tendon).4 The question that naturally arises here in relation to FQAD is why the pain in the Achilles tendon, for example, is so severe after taking ciprofloxacin, levofloxacin and the like, even though there is usually no acute inflammation, such as after a sports injury? Find out more in our article on the causes of tendon pain. (Crosslink article 7: What causes pain in the tendon area?) Next, however, we will discuss the general causes of tendon disorders (Crosslink article 5: Causes of tendon disorders) to deepen our knowledge on the subject of tendons. The question that naturally arises here in relation to FQAD is why the pain in the Achilles tendon, for example, is so severe after taking ciprofloxacin, levofloxacin and the like, even though there is usually no acute inflammation like after a sports injury? Find out more in our article on the causes of tendon pain. Next, however, we will discuss the general causes of tendon disorders in order to deepen our knowledge on the subject of tendons.


Marco Karrer B.Med

Many thanks for their cooperation: Andrea Gall (spelling), Ferdinand Dirsch (SEO, additions, translation into English), Michael Rosar (content, simplifications), Patrick Horisberger (content, simplifications),


First publication: 28.05.2023

Update 15.01.2023



  1. Pathologie das Lehrbuch, G. Höfler, H. Kreipe, H. Moch 6. Aufl. 2019
  2. https://www.sports-health.com/sports-injuries/general-injuries/what-difference-between-tendonitis-tendinosis-and-tendinopathy#footnote1
  3. Tendinopathy: Why the difference between Tendinitis und Tendinosis Matters; 2012
  4. Biology of tendon injury: healing, modeling and remodeling P. Sharma and N. Maffuli; 2006
  5. Pathogenesis of tendinopathies: inflammation or degeneration? Michele Abate et al.
  6. Histologie das Lehrbuch, Ulrich Welsch, Wolfgang Kummer, Thomas Deller Elsevier 5. Auflage 2018
  7. https://www.amboss.com/de/wissen/Tendinopathie
  8. https://de.wiktionary.org/wiki/-pathie#:~:text=%2Dpathie-,%2Dpathie,mit%20der%20Bedeutung%3A%20Methode%2C%20Heilmethode

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