A boutonniere deformity is caused by a disruption of the central slip, which is the primary extensor tendon at the PIP joint. Disruption of the central slip with compromise of the triangular ligament subjects the lateral bands to migration volar to the axis of rotation of the PIP joint. This volar migration allows the lateral bands to act as flexors of the PIP joint. Volar plate injuries, if left untreated, can lead to a pseudoboutonniere deformity. Splinting the PIP joint in extension full time is often beneficial as long as the PIP is passively correctable. Dynamic splinting to increase is often used to increase extension if the deformity is not a fixed contracture.

A boutonniere deformity

Custom boutonniere splint