What characterizes a boutonniere deformity?

A boutonniere deformity is characterized by the specific positioning of the joints in the finger, primarily impacting the proximal interphalangeal (PIP) joint and the distal interphalangeal (DIP) joint. In this condition, there is flexion at the PIP joint while the DIP joint is in extension, which results from a rupture or disruption of the central slip of the extensor tendon.

This particular presentation leads to a characteristic "buttonhole" appearance, hence the name "boutonniere." The flexion of the PIP joint occurs due to the imbalance of the tendon forces, while the DIP joint appears to be hyperextended due to the pull from the intact flexor tendons. Understanding this characteristic positioning is essential for proper diagnosis and treatment, as management may involve splinting, therapy, or surgery to restore function and alignment to the affected digits.