What is the difference between Tendinopathy, Tendonitis and Tendinosis?

Tendinopathy, Tendonitis, Tendinosis are terms that are often used interchangeably to describe pain and dysfunction in tendons, but they actually refer to different conditions.

Tendinopathy:

 A general term used to describe any disorder of a tendon, including tendinitis, tendinosis, and peritendinitis. According to Jill Cook, a prominent tendon expert, tendinopathy is characterised by a combination of pain, swelling, and impaired function, as well as changes to the structure of the tendon at a cellular level (Cook et al., 2016).

Tendonitis:

Specifically refers to inflammation of a tendon. Inflammation is the body's response to injury or infection, and it is characterised by redness, swelling, heat, and pain. However, as Jill Cook points out, recent research has suggested that true tendinitis is actually a relatively rare condition, and that many cases of "tendonitis" are actually tendinosis. 

Tendinosis:

Characterised as a degenerative condition of the tendon due to changes in the structure of the collagen fibres that make up the tendon (Cook et al., 2016). According to Cook and Purdam (2009), tendinosis is caused by a combination of mechanical overload (i.e. excessive or repetitive loading of the tendon), genetic factors, and age-related changes in the tendon. Tendinosis is characterised by the accumulation of disorganised collagen fibres, as well as increased numbers of cells called tenocytes, which are responsible for synthesising and maintaining the collagen fibres. These changes can lead to a weakening of the tendon and an increased risk of rupture.

Other tendon experts have also noted the difference between tendinopathy and tendonitis. For example, Alfredson et al. (2011) note that tendinopathy is a more general term that encompasses both tendinitis and tendinosis, and that the treatment for tendinopathy should be based on the specific underlying pathology of the condition, either acute irritation (tendinitis) or long term mechanical overload or degeneration (tendinosis).

In summary, Tendinopathy is a general term used to describe any disorder of a tendon, while Tendinitis specifically refers to inflammation of a tendon. However, Tendinosis, which is a degenerative condition of the tendon characterised by changes in the structure of the collagen fibres that make up the tendon, is probably more commonly the pathology of most cases a physiotherapist will see and help with recovery.

References:

Cook, J. L., & Purdam, C. R. (2009). Is tendon pathology a continuum? A pathology model to explain the clinical presentation of load-induced tendinopathy. British Journal of Sports Medicine, 43(6), 409–416. https://doi.org/10.1136/bjsm.2008.051193

Cook, J. L., Rio, E., Purdam, C. R., & Docking, S. I. (2016). Revisiting the continuum model of tendon pathology: what is its merit in clinical practice and research? British Journal of Sports Medicine, 50(19), 1187–1191. https://doi.org/10.1136/bjsports-2015-095422

Alfredson, H., Lorentzon, R., & Backman, S. (2011). Tendinopathy: pathology and pathogenesis. Journal of Musculoskeletal and Neuronal Interactions, 11(2), 93–101.