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Tendons Explained

Intrinsic and Extrinsic Factors Associated With Tendinopathy

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Updated June 27, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

What Is a Tendon?

Tendons are fibrous cords of tissue that attach muscles to bones. Tendons transfer force from muscle to bone in order for joints to move. Some tendons, but not all, are covered by a sheath. The inner walls of the sheath produce a small amount of lubrication (synovial fluid), which helps the tendon to move freely.

With aging, tendons become less flexible and elastic, making them more prone to injury. Generally, there are three types of tendon disorders: tendinitis, tenosynovitis, and ganglion cyst. Tendinitis is inflammation of the tendon. Tenosynovitis is inflammation of the tendon sheath. A ganglion cyst is an accumulation of fluid within the tendon sheath.

Tendinopathy, a term that means disorders of the tendons, most commonly involves the rotator cuff (particularly supraspinatus) and biceps brachii tendons in the shoulder, the forearm extensor and flexor tendons in the forearm, the patella tendon in the knee, the Achilles tendon in the lower leg, and the tibialis posterior tendon in the ankle and foot.

What Causes Tendinitis?

Inflammation of a tendon may be caused by repetitive activity, prolonged activity, exertion, awkward posture, static posture (staying in one position for a long time), vibration, or any localized stress. Under these circumstances, the fibers of the affected tendon can tear apart, much like a rope that becomes frayed or unraveled. Over a period of time, inflamed tendons that are not given a chance to heal become thick, irregular, and possibly permanently weakened.

What Causes Tenosynovitis?

Inflammation of the tendon sheath occurs when the lubrication produced is insufficient, either in quantity or quality. Repetitive or prolonged activity, exertion, awkward or static positioning, vibration or localized stress may cause the lubrication system to malfunction, creating friction between the tendon and tendon sheath. Repeated bouts of tenosynovitis can cause the formation of fibrous tissue, thickening of the sheath, and impaired movement of the affected tendon.

What Causes a Ganglion Cyst to Develop?

Ganglion cysts erupt from the capsule of a joint or the sheath of a tendon. A ganglion cyst contains a thick, mucous-like fluid similar to the fluid found in the joint (synovial fluid). Typically, ganglion cysts are found in the wrist or hands, but can occur on the feet as well. Ganglion cysts are often associated with increased activity or repetitive motion.

Intrinsic Causes of Tendinopathy

Aside from extrinsic factors that cause tendinopathy (tendon disorders), researchers have suggested certain intrinsic factors may also be associated, such as metabolic diseases (obesity, diabetes mellitus, high blood pressure, increased serum lipids, and hyperuricemia). High blood pressure has been statistically linked to tendinopathy for women only. Diabetes mellitus has shown a statistical association for men under age 44.

Other diseases that have been found to be associated with tendinopathy include systemic diseases, neurological conditions, infectious diseases, chronic renal failure, psoriasis, systemic lupus erythematosus, hyperparathyroidism and hyperthyroidism. And, as you might expect, tendinopathy may be a consequence of aging in some cases.

Rupture of the extensor tendons of the fingers is a common and disabling complication of rheumatoid arthritis. Tenosynovectomy (surgical removal of the tendon sheath) is highly effective in preventing tendon rupture but it is not easy to identify at-risk patients. Reconstruction of ruptured tendons often fails to restore full movement.

Sources:

Pathogenesis of tendinopathies: inflammation or degeneration? Abate M. et al. Arthritis Research & Therapy. June 30, 2009.
http://arthritis-research.com/content/11/3/235/

Tendon Disorders. Canadian Centre for Occupational Health and Safety. CCOH. December 16, 2010.
http://www.ccohs.ca/oshanswers/diseases/tendon_disorders.html

Ganglion Cysts. E-Hand.com. The Electronic Textbook of Hand Surgery. Accessed July 7, 2012.
http://www.eatonhand.com/hw/hw013.htm

Screening for extensor tendon rupture in rheumatoid arthritis. Rheumatology. Williamson L. et al. October 25, 2000.
http://rheumatology.oxfordjournals.org/content/40/4/420.full

Tenosynovectomy. MediLexicon. Accessed July 12, 2012.
http://www.medilexicon.com/medicaldictionary.php?t=90216

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