A deep laceration or sudden traumatic closed rupture of the central slip of the extensor tendon mechanism precisely at its insertion onto the dorsal base of the middle phalanx (Zone III) inevitably leads to which classic, complex digit deformity if left untreated?

Explanation:
The correct option is a. A Boutonnière (buttonhole) deformity is characterized by flexion of the proximal interphalangeal (PIP) joint and hyperextension of the distal interphalangeal (DIP) joint. When the central slip is disrupted, the head of the proximal phalanx herniates 'like a button through a buttonhole' between the lateral bands. Over time, the lateral bands subluxate volar to the PIP joint axis of rotation, turning them into PIP flexors while concentrating all their extensor pull exclusively on the DIP joint, creating the classic deformity. Reference: Campbell's Operative Orthopaedics. Classic Ortho mcq anatomy question.