Boutonnière deformity is a deformity in which the middle finger joint is bent in a fixed position inward (toward the palm) and the outermost finger joint is bent excessively outward (away from the palm).
(See also Overview of Hand Disorders.)
People with rheumatoid arthritis can develop the disorder because they have long-standing inflammation of the middle joint of a finger.
If the deformity is caused by an injury, the injury usually occurs at the base of a tendon (called the middle phalanx extensor tendon). As a result, the middle joint (called the proximal interphalangeal joint) becomes “buttonholed” between the outer bands of the tendon that runs to the end of the finger. That is, the bones of the joint push out through the bands of the tendon like a button through a buttonhole. The deformity may interfere with hand function.
The doctor makes the diagnosis of boutonnière deformity by examining the finger.
When the Fingers Are Abnormally Bent
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).
Treatment of Boutonnière Deformity
- A splint
- Sometimes surgery
A boutonnière deformity caused by an injury to an extensor tendon (a tendon that pulls the finger up) can usually be corrected with a splint that keeps the middle joint fully extended for 6 weeks. However, the splint will not be effective if scarring and permanent deformities have already developed (usually after many weeks).
When splinting is ineffective, or when boutonnière deformity is due to rheumatoid arthritis, surgery may be needed to improve function.