(See also Overview of Hand Disorders Overview of Hand Disorders Hand and finger disorders include ganglia, deformities, disorders related to nerves or blood vessels, osteoarthritis, trigger finger, Kienböck disease, and infections. Some other disorders that... read more 
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The most common cause of swan-neck deformity is rheumatoid arthritis Rheumatoid Arthritis (RA) Rheumatoid arthritis is an inflammatory arthritis in which joints, usually including those of the hands and feet, are inflamed, resulting in swelling, pain, and often destruction of joints.... read more 
. Other causes include untreated mallet finger Mallet Finger In Mallet finger, the fingertip curls down and cannot be straightened. It is usually caused by a tendon injury. (See also Overview of Sprains and Other Soft-Tissue Injuries and Finger Fractures... read more , looseness (laxity) of the fibrous plate inside the hand at the base of the fingers or of the finger ligaments Ligaments Ligaments are tough fibrous cords composed of connective tissue that contains both collagen and elastic fibers. The elastic fibers allow the ligaments to stretch to some extent. Ligaments surround... read more , chronic muscle spasm affecting the hands caused by nerve damage (called muscle spasticity), other types of arthritis, a ruptured finger tendon Tendons and Bursae Tendons are tough bands of connective tissue made up mostly of a rigid protein called collagen. Tendons firmly attach each end of a muscle to a bone. They are often located within sheaths, which... read more , and misalignment in the healing of a fracture of the middle bone of the finger. Normal bending of the finger may become impossible. The deformity can therefore result in considerable disability.
When the Fingers Are Abnormally Bent
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.
Treatment of Swan-Neck Deformity
Treatment of swan-neck deformity is aimed at correcting the underlying disorder when possible.
Mild deformities that have not yet developed scarring may be treated with finger splints (ring splints), which correct the deformity while still allowing a person to use the hand.
Problems with the ability to pinch can be greatly improved by surgically realigning the joints or by fusing the thumb or finger joints together (called interphalangeal arthrodesis) into positions that allow for optimal function.
