The boutonniere deformity is a bent middle
joint and a hyperextended end joint. Literally, boutonniere means "buttonhole".
The name refers to the typical appearance of the hole in the extensor mechanism
caused by a central slip injury, allowing the head of the proximal phalanx
to poke through. I must admit that I can only remember the spelling (two
"N"s, one "R") by thinking of the word mayonnaise, knowing that it has
the same double letter...
