Boutonnière Deformity (Buttonhole Deformity) By David R Steinberg, MD, Perelman School of Medicine at the University of Pennsylvania Reviewed / Revised Apr 2022 | Modified Sep 2022 View Patient Education Topic Resources Boutonnière and swan-neck... Boutonnière Deformity in... A boutonnière deformity consists of flexion of the proximal interphalangeal (PIP) joint accompanied by hyperextension of the distal interphalangeal (DIP) joint.