boutonnière deformity /bo̅o̅′tônyer″/ [Fr, buttonhole] , an abnormality of a finger marked by fixed flexion of the proximal interphalangeal joint and hyperextension of the distal interphalangeal joint. The central slip of the digit extensor tendon mechanism attenuates or ruptures over the PIP joint, and the associated lateral bands slip below the axis of the joint, thus pulling the PIP into a flexed posture. The condition occurs in rheumatoid arthritis and can occur following trauma to a finger.
