What is tendonitis?

Tendons are thick cords of fibrous material that attach muscles to bone. Tendonitis¹ (also commonly spelled “tendinitis”) occurs when one of these tendons becomes inflamed or irritated.

Any tendon can be affected by tendonitis; however, the most commonly affected areas are the knees, elbows, shoulders, heels, and wrists. These tendons are more susceptible to inflammation because the joints they surround are used so frequently, often in the same kinds of ways. Both frequent use and repeated types of movement can lead to tendonitis.

Tendonitis is referred to by many common names, usually depending on the location and/or common cause of the inflammation. Some of these names include “jumper’s knee,” “golfer’s elbow,” “tennis elbow,” and “pitcher’s shoulder.” Tennis elbow, which refers to tendonitis that occurs in certain tendons in the arm, develops at some point in 40–50%² of people who play racquet sports.

When severe, tendonitis can cause a tendon to rupture, which may require surgery. Most cases of tendonitis, however, go away with sufficient rest and recuperation. Physical therapy, pain relievers, and certain stretches or exercises can also help relieve pain (and, in some cases, speed the healing process) while waiting for a tendon to recover.

Peroneal tendonitis

Peroneal tendonitis³, a particular form of tendonitis, is the result of inflammation in the tendons found behind the outer ankle bone. These tendons, called peroneal tendons, connect this bone to the rest of the foot and work to stabilize the ankle, helping to prevent sprains.

Injuries to the peroneal tendons may be classified as acute (occurring suddenly, often due to an ankle sprain) or chronic (developing slowly over time, usually as the result of overuse and/or repetitive movement).

Achilles tendonitis

The Achilles tendon is the largest tendon in the body. This rope-like tendon runs down the back of the lower leg and connects the calf muscles to the heel bone at the back of the foot.

Despite the Achilles tendon’s ability to withstand a great deal of stress, it is prone to tendonitis caused by overuse or degeneration over time. This form of tendonitis, called Achilles tendonitis, is most commonly caused by sports that require running or frequent jumping and accounts for 15%⁴ of all running-related injuries.

In some cases, Achilles tendonitis may also be caused by an inflammatory disease, such as reactive arthritis, gout, rheumatoid arthritis, or ankylosing spondylitis.

Common symptoms⁵ of this condition include:

• Thickening of the Achilles tendon
• Severe pain the day after exercising (not necessarily during exercise)
• Bone spurs in the heel
• Pain in the Achilles tendon that worsens during use or throughout the day

Achilles tendonitis is more likely to occur in people who have significantly increased the amount of exercise they are doing, those who have tight calf muscles, or those who already have bone spurs that are putting pressure on the tendon.

How common is tendonitis?

Tendonitis is a common⁶ injury. While researchers are not sure of the exact number of people affected by the condition, tendonitis is known to cause at least 70,000⁷ people to miss work each year.

What causes tendonitis?

Tendonitis is most commonly caused⁸ by the long-term repetition of a particular movement. Repetitive motions put stress on the tendons, especially when they aren’t performed properly or when the muscles around the tendon hit a point of fatigue. At that point, the tendon has to start doing the work of the muscles, causing irritation and inflammation. This form of tendonitis often arises as a result of everyday activities, such as work, sports, or hobbies (like working in the garden).

In some cases, a sudden injury can cause tendonitis to develop. Someone with a sprained or broken ankle, for instance, may also end up with tendonitis as a result of their injury.

Tendonitis can also occur as an indirect result of an injury well after it initially occurred. Oftentimes, when a part of the body is in pain, a person is forced to modify their movement patterns to accommodate the injury. When performed improperly, these new movement patterns can put stress on the tendons, leading to tendonitis.

Some people may also develop tendonitis as the result of lifting too heavy of a load. This is especially true if they are lifting the load improperly (with the back instead of the legs) or lifting heavy objects repeatedly.

Using an improper technique on these types of repeated motions can also lead to tendonitis. This can happen due to anything from lifting heavy objects to playing a sport (such as using improper form while swinging a tennis racket).

Risk factors for tendonitis

Certain factors may increase your risk of developing tendonitis. These can be modifiable (changeable, such as occupation or sports) or non-modifiable (inherent or unchangeable, such as age or genetics).

Some major risk factors⁹ for tendonitis include:

• Age: The tendons become less flexible over time, making them more susceptible to tears. In general, people over the age of 40 are at a higher risk for tendonitis than younger people.
• Occupation: Working a job that involves repetitive movements, such as moving or construction, can contribute to tendonitis. Those with jobs that involve awkward positions, overhead reaching, forceful exertion, or vibration are also more likely to be affected by the condition. This is particularly true for older people in such jobs.
• Sports: Most sports involve repetitive motions. Those most likely to cause tendonitis include baseball, golf, racquet sports, basketball, skiing, running, swimming, and bowling. Sports that involve lifting heavy objects, such as weightlifting, powerlifting, and strongman, may also be more likely to cause tendonitis. Some gymnasts may also be more prone to developing tendonitis, as well.
• Certain hobbies or activities: Participation in activities that require repetitive motions, such as gardening, landscaping, shoveling, scrubbing, painting, or woodworking, can lead to tendonitis.
• Poor posture: Poor posture can cause certain parts of the body to be permanently out of place. Having poor posture may make using proper techniques close to impossible, particularly if the poor posture has been a long-term problem. Changing the way that you sit at work or stand at home could make a huge difference in your likelihood of developing tendonitis.
• Certain diseases: Some health conditions, including rheumatoid arthritis, certain blood and/or kidney diseases, and gout (or pseudogout), can cause the muscles to weaken. When the muscles cannot sufficiently bear stress, the tendons are forced to do so instead. Less commonly, tendonitis can occur in people with gonorrhea or diabetes.
• Medications: While rare, certain types of medications, including statins (which are used to treat high cholesterol) and fluoroquinolone antibiotics, can put your tendons at a greater risk of tearing. If you are on one of these medications and are concerned about developing tendonitis, your healthcare provider may recommend a lower dose of medication or a different course of treatment.

Tendonitis symptoms

The most common symptoms¹⁰ of tendonitis include:

• Pain: While most people with tendonitis describe experiencing a dull ache, some cases of tendonitis can cause much more severe pain. In these cases, the pain may feel sharp or like a severe ache.

Generally, tendonitis pain is worse when moving the affected joint than when at rest. In some people, attempting to use an affected tendon and joint can cause pain that is severe enough to prohibit motion and/or use entirely.

• Tenderness: Some cases of tendonitis may cause tendons to be painful to the touch. For most people, however, it will take deeper probing to cause pain to the affected tendon. Additionally, while this deep probing may be painful, it is usually tolerable.
• Swelling: The tendons affected by tendonitis may swell, sometimes enough to be visible above the surface of the skin. This may appear as a lump somewhere along the length of the tendon.

Generally, however, the swelling caused by tendonitis is mild. If severe swelling occurs, it is usually an indication that something else is wrong with the joint (either instead of or along with tendonitis).

• New or unusual sensations: Some individuals with tendonitis may feel grating or cracking sensations in the affected tendon during movement. While this can be disconcerting, it doesn’t necessarily indicate a severe problem.
• Redness: If inflammation is severe enough, the skin surrounding an affected area may turn pink or red.
• Difficulty moving the affected joint: When a tendon becomes severely swollen or irritated, it may become difficult to move the affected joint. This is most common when the space surrounding an affected tendon is limited, forcing it to swell into or up against the joint.

Complications from tendonitis

Especially when left untreated, tendonitis may lead to a number of health complications¹¹, including:

• Increased risk of rupture: Leaving tendonitis untreated increases the likelihood that the affected tendon will partially or completely rupture (tear). A ruptured tendon usually requires surgery to heal.
• Tendinosis: Long-term (chronic) tendonitis can progress into tendinosis, a condition involving degenerative changes in the tendon that causes pain and decreases the tendon’s functioning. Tendinosis also involves abnormal blood vessel growth in the tendon, which can cause it to break down over time.

Seeking prompt treatment for tendonitis is the best way to help heal the tendon and prevent it from worsening or developing complications.