Trigger finger, the _doigt à ressort_ of French authors, may be defined as a peculiar defect in the motions of the digit, consisting, first, of an impediment which obstructs the movement of flexion or of extension, or of both, followed, if the motive force be continued, by a sudden cessation of the resistance, and a brusque, spring-like action that often bears a remarkable resemblance to that which accompanies the opening and closure of the blade of a penknife. The first observation was that of Notta in 1850. A finger attacked by this affection generally lies when at rest in a position of flexion, and by a voluntary effort or by passive force may be straightened, with the peculiar result described in the definition, the resistance to extension suddenly yielding with a trigger- or spring-like action; and the same phenomenon is usually but not necessarily repeated when the digit is again bent. In exceptional cases a reverse condition obtains: the passive finger is kept in a state of extension, and it is during flexion that the trigger phenomenon is elicited. The movement may be merely inconvenient, or it may be more or less painful. The sign may be constant, accompanying every movement, or it may be intermittent, disappearing and recurring without any obvious reason. It is usually confined to a single finger, but it may be multiple. The digits most frequently involved are the middle finger, the ring finger, and the thumb, while the index and little fingers are relatively free, and the right side is more often affected than the left. It is rather more common in women than in men (in the proportion of three to two); and much more frequent in adults than in children, but may appear at all ages. The etiology is ill understood. In many cases an important influence, direct or remote, has been assigned to rheumatism; in others the condition has been attributed to injuries of various kinds; in others to occupations necessitating over-use of the digital articulations (as in sempstresses); but no cause has yet been recognised which can account for any large proportion of the examples.