What characterizes a boutonniere deformity?

A boutonniere deformity is characterized by a specific pattern of finger joint positioning due to an injury or a condition affecting the extensor tendons. In this deformity, there is flexion at the proximal interphalangeal (PIP) joint accompanied by hyperextension at the distal interphalangeal (DIP) joint. This occurs because the central slip of the extensor tendon is disrupted or ruptured, leading to an inability to extend the PIP joint while still allowing the DIP joint to hyperextend. The result is a characteristic "buttonhole" appearance of the finger, which aligns with the description provided by the correct answer choice. Understanding this condition is important in the context of treatment and rehabilitation in orthotics and prosthetics, as managing the joint positions effectively can improve function and reduce pain.