An injury that causes damage to the tendons that straighten the middle joint of a finger results in a condition known as a Boutonnière Deformity. This results in an inability to straighten the middle joint of the injured finger while the fingertip simultaneously bends back on its own. Unless treated quickly, the injury may cause the deformity to progress further to the point of permanence and impaired function.
Boutonnière Deformity mostly occurs from an impact to the top-middle side of a flexed finger joint.
Deep cuts on the top side of the finger can also sever the central tendon from where it attaches to the bone. The name comes from the appearance of the tear in the tendon, as it looks like a buttonhole or “boutonnière” in French. In rare cases, the bone may pop out through the opening.
Arthritis can also cause Boutonnière deformities.