bone, joint, and muscle disorders
Swan Neck Deformity
Introduction
Swan-neck deformity is a bending in (flexion) of the base of the finger, a straightening out (extension) of the middle joint, and a bending in (flexion) of the outermost joint. (See also Overview of Hand Disorders .) The most common cause of swan-neck deformity is Rheumatoid Arthritis (RA) . Other causes include untreated Normal bending of the finger may become impossible. The deformity can therefore result in considerable disability. Some disorders, such as rheumatoid arthritis, and injuries can cause the fingers to bend abnormally. In swan-neck deformity, the joint at the base of the finger bends in (flexes), the middle joint straightens out (extends), and the outermost joint bends in (flexes). In boutonnière deformity, the middle finger joint is bent inward (toward the palm), and the outermost finger joint is bent outward (away from the palm). True swan-neck deformity does not affect the thumb, which has one less joint than the other fingers. However, in a variant of swan-neck deformity, called duck-bill, Z (zigzag) type, or 90°-angle deformity, the top joint of the thumb is severely overstraightened with a bending in of the joint at the base of the thumb to form a 90° angle. If duck-bill deformity and swan-neck deformity of one or more fingers occur together, the ability to pinch can be seriously reduced. A doctor makes the diagnosis of swan-neck deformity by examining the hand and finger. 