**Core Concept**
Swan neck deformity is a type of flexion deformity of the finger, characterized by hyperextension of the proximal interphalangeal (PIP) joint and flexion of the distal interphalangeal (DIP) joint. This deformity results from an imbalance of the extrinsic and intrinsic muscles of the hand.

**Why the Correct Answer is Right**
The swan neck deformity is typically seen in rheumatoid arthritis due to the weakening of the extensor tendons and the intrinsic muscles of the hand. The loss of function of these structures leads to an imbalance, causing the PIP joint to hyperextend and the DIP joint to flex. This deformity can also be caused by other conditions such as central slip rupture in the hand.

**Why Each Wrong Option is Incorrect**
* **Option A:** Osteoarthritis is not typically associated with swan neck deformity, as it primarily affects the DIP joint.
* **Option B:** Trigger finger is a condition characterized by flexion of the finger due to a nodule in the flexor tendon, not a hyperextension deformity.
* **Option C:** Dupuytren's contracture is a condition that causes flexion of the finger due to a palmar fibromatosis, not a hyperextension deformity.

**Clinical Pearl / High-Yield Fact**
The swan neck deformity can be a diagnostic clue for rheumatoid arthritis, especially when combined with other clinical findings such as joint pain, swelling, and morning stiffness.

**Correct Answer: C. Dupuytren's contracture is not the best choice, the correct answer should be Rheumatoid Arthritis.