Trigger finger or Stenosing Tenosynovitis is a condition in which the affected finger or thumb clicks, catches or locks, normally in a bent position, although it may occasionally present as an inability to bend. It is caused by some wear and tear or swelling of the tendon that causes a nodule to form. The tendon runs through a fibrous tunnel, called the A1 pulley, and much like trying to pull a thread through the eye of a needle when there is a knot in it, the nodule catches or locks at the mouth of the pulley.
Trigger finger usually occurs without any obvious cause, but is more common in people with diabetes. It can also be a problem in people with rheumatoid arthritis, but is not caused by osteoarthritis. There is little evidence that it is caused by working with the hands, but heavy activity, such as manual work, gardening, DIY etc. can exacerbate the condition.
The diagnosis of trigger finger is usually made on the history (what you tell the doctor) and examination in clinic. It may very occasionally be necessary to investigate further with x-ray or ultrasound examinations to ensure the diagnosis is correct.