Repeatedly performing hand and thumb motions such as grasping, pinching, squeezing, or wringing may lead to the inflammation of tenosynovitis. This inflammation can lead to swelling, which hampers the smooth gliding action of the tendons within the tunnel. Arthritic diseases that affect the whole body, such as rheumatoid arthritis, can also cause tenosynovitis in the thumb. In other cases, scar tissue from an injury can make it difficult for the tendons to slide easily through the tunnel.