Trigger finger is a painful condition that causes the fingers or thumb to catch or lock when bent. In the thumb its called trigger thumb.

Trigger finger happens when tendons in the finger or thumb become inflamed. Tendons are tough bands of tissue that connect muscles and bones. Together, the tendons and muscles in the hands and forearms bend and straighten the fingers and thumbs.

A tendon usually glides easily through the tissue that covers it (called a tendon sheath) because of a lubricating membrane called the synovium. Sometimes a tendon may become inflamed and swollen. When this happens, bending the finger or thumb can pull the inflamed tendon through a narrowed tendon sheath, making it snap or pop.

Trigger finger happens when part of the tendon in your finger becomes inflamed and swollen. Tendons are long cords that run along the length of each of your fingers, connecting your finger bones to the muscles in your forearms. They allow you to move your fingers. Your tendons are kept in place by strong bands of tissue, called pulleys, which form a tube called a tendon sheath. Your tendons should move smoothly in and out of the tendon sheaths as you bend and straighten your fingers.

If one of your tendons becomes inflamed, it may catch on the opening of the tendon sheath at the base of your finger. This catching can cause a clicking sensation and your finger can sometimes gets stuck (locked) in a bent position.

Around three in 100 people are affected by trigger finger. It most often affects your thumb (trigger thumb) followed by your ring, middle, little and index fingers. Several of your fingers can be affected at one time.

Trigger finger is more common in women than men. People of any age can get it (including children) but most people who get trigger finger are between 50 and 60.