Definition: A boutonniére deformity is a finger condition that prevents you from being able to fully straighten your finger. Three finger joints can be seen when you make a fist. In a boutonniére deformity, the joint in the middle is held in a slightly flexed (bent) position, while the joint at the tip of the finger is hyperextended (beyond straight).
The reason a boutonniére deformity occurs is due to tendon damage on the back of the finger. When not functioning normally, the tendons prevent the finger from fully straightening. The most common causes of a boutonniére deformity are either an untreated tendon injury, or rheumatoid arthritis of the fingers.
The name boutonniere deformity comes from the French word meaning buttonhole. One cause of a boutonniere deformity is an injury to the tendon that looks like a buttonhole in the tendon.
Source:
Boyer MI and Gelberman RH "Operative correction of swan-neck and boutonniere deformities in the rheumatoid hand" J. Am. Acad. Ortho. Surg., Mar 1999; 7: 92 - 100.
