Tendons are fibrous cords of tough tissue that connect muscles to bones. Some tendons are surrounded by tendon sheaths. (See also Introduction to Muscle, Bursa, and Tendon Disorders.)
The cause of tendinitis is often unknown. Tendinitis usually occurs during middle or older age, as the tendons weaken and become more susceptible to injury and inflammation. (Weakening of the tendon, called tendinopathy, usually results from many small tears that occur over time. Affected tendons may gradually or suddenly tear completely.) Tendinitis also occurs in younger people who exercise vigorously (who may develop rotator cuff tendinitis—see also Rotator Cuff Injury/Subacromial Bursitis) and in people who do repetitive tasks.
Certain tendons are particularly susceptible to inflammation:
Tendons of the shoulder (rotator cuff): Inflammation of these tendons is the most common cause of shoulder pain (see Rotator Cuff Injury/Subacromial Bursitis).
The two tendons that extend the thumb away from the hand: Inflammation of these tendons is called De Quervain syndrome.
The flexor tendons that clench the fingers: Inflammation causes these tendons to get caught in their sheaths, resulting in a popping feeling (trigger finger).
The tendon above the biceps muscle in the upper arm (bicipital tendon): Pain can occur when the elbow is bent or the arm is elevated or rotated.
Achilles tendon in the heel: Pain occurs at the back of the heel (Achilles tendinitis).
A tendon that runs over the side of the knee (popliteus tendon): Pain occurs on the outer part of the knee.
Tendons near the hip bone (trochanter): Because bursae may also be affected, the term trochanteric bursitis is often used to include inflammation of these tendons.
Some antibiotics, such as fluoroquinolones, may increase the risk of tendinopathy (weakening of the tendon) and rupture of the tendon.
Certain joint diseases, such as rheumatoid arthritis, systemic sclerosis, gout, diabetes, and reactive arthritis (previously called Reiter syndrome), can increase the risk of tenosynovitis. In people with gonorrhea, especially women, gonococcal bacteria can cause tenosynovitis, usually affecting the tissues of the shoulders, wrists, fingers, hips, ankles, or feet.
The inflamed tendons are usually painful when moved or when pressed. Moving the joints near the tendon, even a little, may cause pain, depending on how severe the tendinitis is. Occasionally, the tendons or their sheaths swell and feel warm.
If tendinitis lasts a long time, calcium may become deposited. The area around the shoulder joint is often affected. In addition to being painful, the shoulder may feel stiff and weak. It may snap or catch when moved.
Sometimes corticosteroids (such as betamethasone, methylprednisolone, or triamcinolone) and anesthetics (such as lidocaine) are injected into the tendon sheath. Rarely, the injection causes pain hours later because the corticosteroid temporarily forms crystals inside the joint or sheath. This pain lasts less than 24 hours and can be treated with cold compresses and pain relievers.
Other drugs may be used, depending on the cause. For example, if gout is the cause, indomethacin or colchicine may be used.
After inflammation is controlled, exercises to increase the range of motion should be done several times a day.
Chronic, persistent tendinitis can occur in rheumatoid arthritis and may have to be treated surgically to remove inflamed tissues. Physical therapy may be needed after surgery, and surgery is occasionally needed to remove calcium deposits or repair the tendon from areas of long-standing tendinitis, such as the area around the shoulder joint. Occasionally, surgery is done to release scars that limit function or to remove part of a bone that is rubbing against a tendon.
Rotator cuff tendinitis (see Rotator Cuff Injury/Subacromial Bursitis) is the most common cause of shoulder pain. It causes pain when the arm is raised (particularly between 40° and 120°) or when people dress. People often have pain during the night, especially when they lie on the affected arm.
Symptoms of rotator cuff tendinitis may occur suddenly and be severe, especially after physical activity, or they may develop more slowly and be milder.