A closed boutonniere finger results from a mechanism similar to that of a mallet in that there is a tear of the insertion of the extensor mechanism to the dorsal base of the phalanx (Fig. 18). However, unlike the mallet, the extensor mechanism continues past the proximal interphalangeal joint, and a tear in the tendon mechanism at this point resembles a buttonhole ("boutonniere"), with the protruding head of the proximal phalanx forming the "button". This alters the normal distribution of tension over the extensor mechanism sheet, allowing the force of proximal pull on the mechanism to bypass the proximal interphalangeal joint, leaving it flexed and diverting it to the distal joint, which becomes hyperextended. Acutely, these injuries are best treated closed with four to six weeks of "4-point" finger splinting to maintain the proximal interphalangeal joint in exten sion and slightly flex the distal interphalangeal joint, allowing flexion of the distal interphalangeal joint. Residual deformity is often more of a cosmetic than functional problem. Typically, the injury is a pure soft tissue mechanism. Boutonniere associated with a dorsal avulsion fracture should be considered a volar fracture dislocation and may be associated with palmar subluxation of the middle phalanx.