What is the difference between boutonnière deformity and pseudo boutonnière deformity?

What is the difference between boutonnière deformity and pseudo boutonnière deformity?

Pseudo boutonnière deformity and boutonnière deformity may look similar, but they aren’t quite the same. The PIP joint is affected in both conditions. However, with pseudo boutonnière deformity, the injury is to the volar plate, or the ligament underneath the joint. The DIP joint will move if you move it.