What causes Boutonnière Deformity?

Boutonnière Deformity is primarily caused by a rupture in the central tendinous slip of the extensor hood, which is a critical structure that allows for the extension of the fingers. When this slip is damaged, it results in an inability to extend the proximal interphalangeal (PIP) joint while the distal interphalangeal (DIP) joint remains flexed. This characteristic positioning leads to the appearance of a boutonnière or "buttonhole" in the finger.

In understanding the context of the other options, overuse of the wrist muscles does not directly cause deformations associated with the extensor mechanism in the fingers. Similarly, weakness of the proximal phalanx or excessive stretching of the flexor tendons are not mechanisms that would lead to the specific complications seen in Boutonnière Deformity. Instead, they may contribute to different types of hand or finger dysfunction but do not directly cause the characteristic changes associated with this particular deformity. The specific nature of the rupture in the extensor hood demonstrates the particular pathophysiological process leading to the change in finger posture seen in this condition.