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Tendinitis and Tenosynovitis

Person holding knee showing xray image of knee red with pain

What is a Tendon?

A tendon is tissue that attaches muscle to the bone. It is flexible, tough and fibrous and it can withstand tension. A ligament extends from bone to bone at a joint, while a tendon extends from muscle to bone.

Tendons and muscles work together and exert a pulling force. Tendons and ligaments are tough and fibrous, but they are known as soft tissue because they are soft compared with bone.

If the sheath around the tendon becomes inflamed, rather than the tendon itself, the condition is called tenosynovitis. Tendinitis and tenosynovitis can occur together.

Tendinitis is the inflammation of the tendon and results from micro-tears that happen when the musculotendinous unit is acutely overloaded with a tensile force that is too heavy and/or too sudden. Tendinitis is still a very common diagnosis, though research increasingly documents that what is thought to be tendinitis is usually tendinosis.

What is Tendinosis?

Tendinosis is a degeneration of the tendon’s collagen in response to chronic overuse; when overuse is continued without giving the tendon time to heal and rest, such as with repetitive strain injury, tendinosis results. Even tiny movements, such as clicking a mouse, can cause tendinosis when done repeatedly.

The confusion about the difference between tendinitis and tendinosis is widespread. Many injuries commonly presumed to be tendinitis are actually tendinosis. For example, tennis elbow is usually described as tendinitis of extensor carpi radialis brevis; however, “signs of either acute or chronic inflammation have not been found in any surgical pathologic specimens in patients with clinically diagnosed lateral tennis elbow syndrome,” proving that tennis elbow is not tendinitis. The histology of tennis elbow shows that it is actually tendinosis.

A microscopic view of tendinosis reveals an increase of immature type III collagen fibers (mature type I fibers dominate in healthy tendon tissue); loss of collagen continuity so that collagen fibers are no longer aligned with each other and sometimes fail to link together to facilitate load-bearing; an increase in ground substance (the material between the body’s cells); and a haphazard increase of vascularization.

These vascular structures “do not function as blood vessels” and “are not associated with increased healing.” The appearance of the tendon shifts from a reflective, “white, glistening and firm” surface to a “dull-appearing, slightly brown and soft” surface (mucoid degeneration).

These changes result in a loss of strength in the tendon and increase the bulk of the tendon, both of which contribute to the cycle of injury and can set the stage for secondary conditions, such as tendinitis and nerve impingement.

The study leads one to believe that, in the forearm and wrist, tendinosis can result in secondary carpal tunnel syndrome; this is because of the thickening of the tendons with excess ground substance and the swelling of the surrounding tissue crowds and compresses the median nerve. There is a prevalent supposition that tendinosis begins with tendinitis, which then instigates a healing process that changes the collagen and weakens the tendon, becoming tendinosis. Perhaps this supposition exists because the stages of soft-tissue healing are generally listed as, in short: inflammation response, regeneration (collagen production), and remodeling (strengthening the collagen in the direction of the forces placed upon it).

In one article, tendinitis is cited as the first stage of a tendinopathy; tendinosis is cited as the second stage and rupture as the third stage. The fourth stage is described as a combination of stages 2 and 3, along with fibrosis and calcification. The suggestion that tendinitis precedes tendinosis is at odds with the fact that a healthy tendon is up to twice as strong as the muscle, making the body of the tendon unlikely to tear before the muscle unless the tendon has already been weakened by degenerative changes.

The idea that tendinitis is the first stage of tendinosis seems to presume that micro-tears and inflammation are a precursor to collagen degeneration. Histopathologic analyses show that torn fibers, scar tissue, and calcification are only found in conjunction with tendinosis some of the time, and inflammatory cells are rarely found in conjunction with tendinosis, supporting the hypothesis that tendinitis occurs secondarily to tendinosis. Excessive and/or repetitive tensile forces on the tendon are likely what instigate the chemistry of degenerative changes associated with tendinosis.

Arnoczky et al. have reportedly shown that tensile forces placed on the tendon are directly related to persistent activation of a stress-activated protein kinase (c-Jun N-terminal kinase (JNK)); the persistent activation of JNK has been related to the initiation of programmed cell death.

This article is an excerpt from Tendinopathy: Why the Difference Between Tendinitis and Tendinosis Matters by Evelyn Bass, LMT. For the full article and references, visit

My additional comments about treatment options.

Acupuncture and Chiropractic Care for Tendinopathy

Acupuncture works by decreasing inflammation in the affected tendon, while helping manage pain. Tendonitis often becomes chronic for many sufferers, but a series of acupuncture treatments can bring relief. Because tendon irritation brings degeneration to the tendon, the injury needs a fresh blood supply and adequate oxygenation for healing. Acupuncture does just that, and also brings pain relief as you heal.

Once your tendonitis responds to treatment, education is offered for proper body mechanics, so you will not suffer the same injury again. Most tendonitis injuries respond to treatment twice a week for three weeks, and a monthly treatment may be helpful to some patients to prevent further tendonitis.

Depending on the level of inflammation, your chiropractor may incorporate techniques such as, ice, bracing, electrical muscle stimulation to help soften the tendons, and or Cold Laser Therapy, which is very effective at reducing inflammation. These first steps are crucial and the mark of an experienced chiropractor.

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