When the tendon develops a nodule or swelling of its lining, it has difficulty passing through the pulley (which is not elastic, but fixed in diameter). The "popping" or "catching" feeling in the finger or thumb comes from the tendon "squeezing" through and giving as it makes it past the pulley. The swollen tendon is irritated more as it has to be squeezed through the pulley, producing more swelling. A vicious cycle of triggering, inflammation, and swelling. Sometimes the finger will become stuck (locked) and it may be hard to straighten or bend the finger. This is like having a finger swell and not being able to get your ring off.
So what causes this condition. Repetitive grasping of objects or an injury to the palm may irritate the flexor tendons. Medical conditions such as rheumatoid arthritis, gout, and diabetes may create swelling around the tendons which then lead to the "vicious" cycle of irritation/inflammation/swelling. Sometimes the cause is not clear.
So the goal of treatment is to eliminate the catching or locking and allow movement without discomfort. To do this the swelling around the tendon must be reduced to allow smooth gliding of the tendon. Wearing a splint or taking anti-inflammatory medication by mouth or injection into the area around the tendon (a corticosteroid shot) are ways to reduce the swelling. Changing how the hand is used, better body mechanics to reduce the impact or repetitive motions helps. If nonsurgical forms of treatment do not improve symptoms, then surgery may be recommended. This surgery is usually performed on an outpatient basis. Most often it is done using local anesthesia, but a regional (where only the arm is numbed) or a general may be used. The surgery cuts the pulley (only one and the finger still has other pulleys to keep it near the bone) which gives the tendon more room to glide, removing the restriction (cutting the ring off the swollen finger). Active motion of the finger is generally begun immediately after surgery. Normal use of the hand can be resumed once comfort permits.