Trigger finger, or trigger thumb, is a type of stenosing tenosynovitis (specifically igital tenovaginitis stenosans) in which the sheath around a tendon in a thumb or finger becomes swollen, or a nodule forms on the tendon. In such a condition, repetitive forceful use of a digit leads to narrowing of the fibrous digital sheath in which it runs. This leads to stenosis of the osseo-fibrous tunnel of the finger. If tendons of the flexor digitorum superficialis or flexor digitorum profundus muscles become enlarged proximal to the tunnel, the affected individual is unable to extend his/her finger. Affected digits may become painful to straighten once bent, and may make a soft crackling sound when moved. More than one finger may be affected at a time, though it usually affects the thumb, middle, or ring finger. The triggering is usually more pronounced in the morning, or while gripping an object firmly.