Trigger Finger

Trigger finger is an inflammation of tissue inside your finger or thumb. It is also called tenosynovitis (ten-oh-sin-oh-VY-tis). Tendons (cordlike fibers that attach muscle to bone and allow you to bend the joints) become swollen. So does the synovium (a slick membrane that allows the tendons to move easily). This makes it difficult to straighten the finger or thumb. 

Causes

Repeated use of a tool, such as a drill or wrench, can irritate and inflame the tendons and the synovium. So can arthritis or an injury to the palm of the hand. But often the cause of trigger finger is unknown.