Which of the following conditions is characterized by limited range of motion at the PIP joint with hyperextension?

Swan neck deformity is a condition characterized by hyperextension at the proximal interphalangeal (PIP) joint while the distal interphalangeal (DIP) joint is flexed. This characteristic appearance is often seen in conditions such as rheumatoid arthritis, where the collagen and connective tissue are affected, leading to alterations in the normal alignment and function of the finger joints.

The specific mechanism involves the weakening of the volar plate at the PIP joint and the imbalance between the flexor and extensor tendons, which allows for the hyperextension at the PIP joint to occur while the DIP joint flexes. In contrast to other conditions, such as a boutonniere deformity where the PIP joint is flexed and the DIP joint is hyperextended, or Dupuytren's contracture which involves a thickening and shortening of the palmar fascia resulting in finger flexion, the swan neck deformity distinctly features this hyperextension at the PIP with a flexed DIP.

Understanding the mechanics and clinical presentation of swan neck deformity is crucial for diagnosis and management, as it informs treatment strategies, including splinting and hand therapy aimed at restoring normal joint function and preventing further contractures.