Boutonniere deformity

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Overview
Boutonniere deformity refers to a finger which is bent in a particular way: bent toward the palm at joint nearest the knuckles, and bent back away from the palm at the joint furthest from the knuckles (hyperflexion at the proximal interphalangeal joint with hyperextension at the distal interphalangeal joint.

Causes are injury, inflammatory conditions like rheumatoid arthritis.

Stages

 * 1) Mild extension lag, passively correctable
 * 2) Moderate extension lag, passively correctable
 * 3) Mild flexion contracture
 * 4) Advanced flexion contracture

Higher numbers indicate a more severe problem and greater likelihood of a poor final outcome

Pathophysiology
This is a flexion deformity of the proximal interphalangeal joint, due to interruption of the central slip of the extensor tendon. This makes it difficult or impossible to extend the proximal interphalangeal joint. The lateral slips separate and the head of the proximal phalanx pops through the gap like a finger through a button hole and the distal joint is drawn into hyperextension. It is often seen with trauma or rheumatoid arthritis.