Tendons are tissues that connect muscles to bone. The muscles that move the fingers and thumb are in the forearm. Long tendons extend from these muscles through the wrist and attach to the small bones of the fingers and thumb. Swelling of the tendons results in friction and pain with certain thumb and wrist movements. Symptoms of tendonitis include swelling on the thumb side of the wrist, pain in the wrist and up the forearm, snapping sensation when moving the thumb, and difficulty moving the thumb and wrist.