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Tendinitis and Tendinosis

Last Updated: Mar 1, 2019


Tendons are cord-like bands of tissue that connect muscles to bone. Tendon tissue is made of a tough, fibrous substance called collagen that can withstand quite a bit of force and tension. However, severe forces or repetitive force over time can cause tiny “microtears” in tendon tissue, leading to injury.

extensor carpi radialis brevis and posterior of elbow joint

Tendinitis is inflammation (redness, swelling, heat, soreness) that occurs when the body’s immune system detects an injury and responds. In the case of tendinitis (also spelled ‘tendonitis’), the body increases the flow of blood and infection-fighting substances to the injured tendon.

Tendinosis is a degenerative injury to the tendon that doesn’t provoke an immune response. It occurs when repetitive, unrelenting stress over time causes the breakdown of collagen, growth of abnormal blood vessels, and thickening of the tendon’s sheath (covering). Research suggests that many injuries diagnosed as tendinitis are actually tendinosis.

Tendon injuries occur in all parts of the body, but are most common in these parts:

Many common sports afflictions, including tennis elbow, swimmer’s shoulder, and jumper’s knee are actually forms of tendinitis/tendinosis.

Tendon injury usually isn’t serious in itself. On the other hand, weakened tendons increase a person’s risk of further injuries, like sprains. In severe cases, the tendon may rupture (tear) and require surgical repair.


Sudden, severe trauma can damage the tendons instantly. However, most tendon injuries are caused by repetitive injury. Even a relatively minor stress can tear and degrade the tendon tissue if it’s repeated over and over. Examples include:

Poor posture and form during these repeated movements can increase stress on the tendons and make injury more likely.

In unusual cases, tendinitis/tendinosis is caused by infection or a reaction to medication.

The incidence of tendon injury increases with age, and it’s especially common after age 40. Some medical conditions can increase the risk, including arthritis, gout, and thyroid disorders.


Symptoms of a tendon injury usually occur near a joint at the attachment point between the bone and muscle.

The first sign is often dull, aching pain that worsens with movement. The affected area is frequently tender to the touch. Some mild swelling may be present.

People with tendinitis of the shoulder may notice an occasional “snapping” sound during movement and may experience freezing (loss of motion) in the shoulder joint.


Tendon injury is usually mild and doesn’t require a doctor’s care. To care for tendinitis/tendinosis at home:

See a doctor if:

A physician can usually diagnose tendinitis based on a patient’s history and physical exam. Imaging tests such as ultrasound, X-ray, or MRI may be ordered to rule out other types of injury. Blood tests can detect infection, which is a rare cause of tendon injury.


Treatment for severe or persistent tendinitis may include:

With proper management, most tendon injuries improve within a few weeks, though some take several months to heal.


To protect your tendons from injury:


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Tina Shahian, PhD

Tina is a writer for Innerbody Research, where she has written a large body of informative guides about health conditions.


A communication specialist in life science and biotech subjects, Tina’s successful career is rooted in her ability to convey complex scientific topics to diverse audiences. Tina earned her PhD in Biochemistry from the University of California, San Francisco and her BS degree in Cell Biology from U.C. Davis. Tina Shahian’s Linkedin profile.


In her spare time, Tina enjoys drawing science-related cartoons.