What is a tendon?

A tendon is a tough piece of tissue that connects a bone to a muscle. When muscles contract, tendons pull on bones to allow movement.

For example, the muscles on the back of the forearm extend the wrist and fingers via tendons that can be clearly seen on the back of the hand.

Tendons that bend joints are known as flexors and those that straighten joints are known as extensors.

Most tendons are at least partly covered by a sheath, the synovium, which makes a tiny amount of oily fluid. This sheath helps the tendon to lie flat along the bone, and the oil allows it to glide freely and smoothly.

Tendons, like ligaments, are largely composed of a tough protein called collagen. Tendons are not metabolically active, so they do not have a good blood supply and consequently healing after a tendon injury can be very slow.

Types of tendon injury

Common tendon injuries can be known either by the sport that usually causes them or the tendon that is affected:

• Tennis elbow (lateral epicondylitis)
• Golfer's elbow (medial epicondylitis)
• Achilles tendonitis
• Wrist tendonitis

What causes a tendon injury?

Tendonitis and tenosynovitis are common types of tendon injury. They often occur together and are sometimes combined in the term tendinopathy.

• Tendonitis is inflammation of a tendon
• Tenosynovitis is inflammation of the sheath that surrounds a tendon

Tendon injuries usually occur when tendons are overused, by playing a lot of sport, for example, or overuse at work. Tenosynovitis commonly occurs around the wrist, leading to tennis elbow.

Continuous writing, typing, assembly line work, etc. can trigger inflammation in the wrist tendon, a condition known as repetitive strain injury (RSI).

Other causes of tendon injury

Tendon injuries can also occur without any overuse. Some types of arthritis such as rheumatoid arthritis can sometimes cause inflammation of tendon sheaths as well as joints.

This causes additional symptoms with joint pains and swelling as well as symptoms of tendon injury.

Infection can also be a cause of tendon injury, though this is rare. A cut or puncture wound to the skin over a tendon may allow bacteria to get in to infect the tendon and/or the tendon sheath.

Occasionally, infection spreads to the tendon sheath from other parts of the body via the bloodstream.

For example, people with gonorrhoea, a sexually transmitted disease, have been known to develop tenosynovitis as a complication.

What are the symptoms of a tendon injury?

The main symptom is simply pain. The joint or tendon itself can be painful. It may be worse at night or during movement/activity.

A tendon injury caused by wear, tear or trauma will usually cause pain that is localised, not that is present in several joints.