The development of a fibrotic nodule along the tendons that flex the hand, which catches under the pulleys of the digit.
Along the length of your fingers are a series of pulleys, which act like the guides on a fishing pole. The pulleys keep the tendon back against the bone of the finger. When trying to bend the finger, the trigger nodule is pulled down tight against one of these guides and snags. With continued force applied, it suddenly snaps under to the other side of the guide, making the finger trigger. The finger becomes stuck in the down position unless manually moved back.
Because of the fibrotic nodule, bending required continued effort, and eventually the finger snaps down into place. This is painful, and often you may not be able to extend the finger back again with muscle power alone, requiring you to use the other hand.
Conservative treatment usually starts with partially immobilizing the finger and preventing it from flexing down too far, preventing further aggravation of the condition. If immobilized and given time to heal, the nodule may resolve itself. Activity modifications are recommended to avoid repetitive and hard gripping. The therapist will also perform passive range of motion exercises. He or she will move your finger for you. This will keep the joints movable and prevent stiffness from developing while the finger is immobilized.