Hi everyone. This is just a mnemonic post on RA deformities.
So there are 2 important deformities that are definitely seen clinically but are hard to remember.
The Boutonniere and the Swan neck deformities both occur as some defect at 3 joints :
The Proximal Interphalangeal Joint (PIP) and the Distal Interphalangeal Joint (DIP) and Metacarpophalangeal Joint (MCP).
So Remembering one of them is sufficient as the other one would be the exact inverse.
So Out one Ex .
Which means there's extension at DIP (the outer joint). Now after extension , alternate the next joint with flexion ( so Flexion at PIP ) followed by extension again ( so extension at MCP )
So , Boutonniere is -
DIP - Extension (out one is ex)
PIP - Flexion
MCP - Extension.
And Swan neck would be the opposite :
DIP - Flexion
PIP - Extension
MCP - Flexion
Hope this helped !