Also known as stenosing tenosynovitis, this condition occurs when inflammation within the tendon sheath causes fingers to painfully lock when you bend them. A majority of the time, this condition is caused by repetitive stress, but you may be more likely to develop a trigger finger if you have diabetes, arthritis, or if you use excessive finger and thumb motions on a daily basis. In severe cases of trigger finger, your finger may completely lock up, meaning you cannot straighten it at all.