- flexion contracture of a proximal interphalangeal (PIP) joint
- extension of a distal interphalangeal (DIP) joint
Boutonnière deformities occur when the central slip of the extensor digitorum tendon is torn or stretched resulting in PIP joint flexion. Increasing PIP joint flexion causes further extensor retinaculum damage resulting in "buttonholing" of the proximal phalanx between the lateral bands of the extensor tendon. Secondary DIP joint extension then occurs .
History and etymology
"Boutonnière" is French for buttonhole. The appearance apparently reminded (presumably French-speaking) surgeons of a buttonhole.