Trigger finger is a type of tenosynovitis. The tendons of the thumb and each of the fingers pass through a sheath on the palm side of the hand. Certain diseases and overuse activities can cause a thickening of this sheath. As the tendon passes through a thickened sheath, the tendon eventually becomes irritated and swells. Pain, catching, and eventually locking of the finger will occur. Early treatment consists of anti-inflammatory medication or Cortisone injection. If these fail to provide relief, the sheath is opened surgically through a small incision at the base of the finger.