Tendons are tough, flexible, fibrous bands of tissue that connect muscles to bones. When tendons become inflamed, irritated or suffer microscopic tears, the condition is called tendonitis. Tendons can be small, like the delicate, tiny bands in the hands, or large, like the heavy, ropelike cords that anchor the calf or thigh muscles. In most cases, the cause of tendonitis is unknown; when a cause can be identified, the condition usually happens for one of two reasons:
- Overuse – A particular body motion is repeated too often.
Overload – The level of a certain activity, such as weightlifting, is increased too quickly.
Rarely, tendonitis is caused by an infection, such as gonorrhea. Tendonitis is most common in the shoulder, elbow, knee, wrist and heel, although it can happen anywhere that tendons are found in the body. For uncertain reasons, tendonitis is also common in people with diabetes. In recent years, a rare cause of tendonitis (or other tendon disease, including rupture) has been recognized: the use of certain antibiotics, including ciprofloxacin or levofloxacin. Why this happens is unknown.
Tendonitis in the shoulder – The most common form of tendonitis in the shoulder is rotator cuff tendonitis. It involves the tendon of the supraspinatus muscle, which attaches to the upper portion of the upper arm bone (humerus) at the shoulder joint. Less commonly, the tendon of the infraspinatus muscle or other tendons of the rotator cuff is affected. In most cases, the supraspinatus tendon is injured by overuse, typically in an occupation or sport that requires the arm to be elevated repeatedly. People at risk include carpenters, painters, welders, swimmers, tennis players and baseball players. The average patient is a male laborer older than 40, and the shoulder pain is on the same side as his dominant hand (for example, right shoulder pain in a right-handed person).
Tendonitis in the elbow – Two forms of tendonitis commonly involve the elbow: lateral epicondylitis and medial epicondylitis. Both are very common overuse injuries among athletes involved in golf or throwing and racquet sports.
Lateral epicondylitis (tennis elbow) causes pain on the outer side of the elbow joint. This condition probably affects 40% to 50% of all adult athletes who play racquet sports. It also can be caused by any activity that repeatedly twists and flexes the wrist, such as pulling weeds, using a screwdriver or even carrying a briefcase.