(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
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.