Causes
The most common causes of tendinitis are strain; overexertion; injury; repetitive movements; and sudden, unaccustomed movements. Tendinitis is most common in seniors and middle-aged people, since the tendons of older individuals lack the elasticity of younger people and have sustained hundreds of microscopic tears due to wear-and-tear over the years.
There are certain diseases that can cause tendinitis, such as rheumatoid arthritis, gout, Reiter's syndrome, lupus, and diabetes. Sometimes, people with gout have uric acid crystals that appear in the tendon sheath that cause friction and tearing. Very high blood cholesterol levels may also be linked with this condition.
Some common types of tendinitis include the following:
Rotator cuff tendinitis affects tennis players, swimmers, and anyone who frequently lifts their arms above the head and in a forward motion. This causes several shoulder tendons to rub together. Inflammation can set in and, if severe and untreated, may start to erode the tendons. Rotator cuff tendons hold the upper arm bone in the shoulder socket.
Achilles tendinitis involves the strongest tendon in the body, the one that connects the heel to the leg muscles. It's usually caused by running uphill or downhill, jumping, or engaging in sports that require sudden stopping and starting. Wearing shoes with either very soft-padded heels or very stiff soles, especially for someone whose ankles roll in, may also contribute to Achilles tendinitis.
Flexor digital tenosynovitis (trigger finger) may be seen in people with rheumatoid arthritis and diabetes. A protrusion or thickening of the tendon catches in the tendon sheath, causing the finger to bend and stick.
De Quervain's tenosynovitis (De Quervain's syndrome) affects the tendon sheaths extending from above the wrist to the thumb. The most common cause is excessive wringing of the wrist or other repetitive movements. In some cases, rheumatoid arthritis may be involved.