Health Questions and Answers

Question: What mechanisms underlie the classic swan neck deformitiy?

Answer:

The swan neck deformity describes flexion at the MCP and DIP joints with extension at the PIP joints. This deformity results from inflammation and subsequent contraction of interosseous and flexor muscles and tendons. Other contributing factors include tenosynovitis and destruction leading to MCP subluxation. Flexion at the MCP leads to exaggerated pull on the extensor tendon of the PIP. The flexion at the DIP is caused because the pull of the flexor tendon overcomes the pull of the extensor tendon.

Reference:  Resnick D (ed): Diagnosis of Bone and Joint Disorders, 4th ed. Philadelphia, W.B. Saunders, 2002

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