Trigger finger is caused by the thickening of rings that surround the tendons that move the fingers from straight to bent and back. The rings are like a tunnel through which the tendons slide back and forth. If the rings thicken, they begin to put pressure on the tendon and sometimes block it from moving. If the person with the trigger finger manages to move it, the tendon may “catch” on a ring, causing that pulling or snapping feeling.
As for risk factors, it’s been found that more women develop trigger finger than do men and people with chronic health issues, like rheumatoid arthritis, diabetes, hypothyroidism (underactive thyroid) seem to be at a higher risk of developing the condition. As well, if you constantly have a grip on an instrument, be it a musical instrument or a tool, the constant bending of the finger could contribute to developing trigger finger.