The fluid known as the tenosynovium is responsible for keeping the sheath constantly lubricated to insure flexor tendons slide smoothly. When the sheath narrows, it blocks the tenosynovium in the process causing painful movements through the sheath and at times halting the finger all together into a bent position. If the current circumstance continues, the tendon could develop scaring, escalating the problem. Rheumatoid arthritis, diabetes, hypothyroidism, amyloidosis are a factor of developing trigger finger. Women are much more likely in developing trigger finger then men are.
Trigger finger (also called stenosing tenosynovitis) occurs when inflammation builds up within a tendon of a finger and causes it to involuntarily flex.  If the condition is severe, the finger gets stuck in a bent position and sometimes makes a snapping sound when forcibly straightened -- sort of like cocking the trigger of a gun, which explains the name. People whose job requires repetitive gripping are at higher risk of developing trigger finger, as are those with arthritis or diabetes. The treatment varies depending on severity and cause, which is why an accurate diagnosis is important.