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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).
This disorder most often results from rheumatoid arthritis (see Rheumatoid Arthritis (RA)) but can also result from injury (such as deep cuts, joint dislocations, or fractures) or osteoarthritis (see Osteoarthritis (OA)). 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 can, but need not, interfere with hand function. The doctor makes the diagnosis by examining the finger.
When the Fingers Are Abnormally Bent
A boutonnière deformity caused by an extensor tendon injury can usually be corrected with a splint that keeps the middle joint fully extended for 6 weeks. The splint will not be effective if scarring and fixed deformities develop (usually after many days or weeks). When splinting is ineffective, or when boutonnière deformity is due to rheumatoid arthritis, surgery may be needed to improve function.
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