musculoskeletal and connective tissue disorders
Swan Neck Deformity
Introduction
A swan-neck deformity consists of hyperextension of the proximal interphalangeal (PIP) joint, flexion of the distal interphalangeal (DIP) joint, and sometimes flexion of the metacarpophalangeal (MCP) joint. (See also Overview and Evaluation of Hand Disorders .) Although characteristic in Rheumatoid Arthritis (RA) , swan-neck deformity has several causes, including untreated Treatment of swan-neck deformity is aimed at correcting the underlying disorder when possible (eg, correcting the mallet finger or any bony malalignment, releasing spastic intrinsic muscles). Mild deformities in patients with rheumatoid arthritis may be treated with a functional ring splint. Severe disability may require surgical treatment. True swan-neck deformity does not affect the thumb, which has only one interphalangeal joint. However, severe hyperextension of the interphalangeal joint of the thumb with flexion of the metacarpophalangeal (MCP) joint can occur; this is called a duck bill, Z (zigzag) type, or 90°-angle deformity. With simultaneous thumb instability, pinch is greatly impaired. This deformity can usually be corrected by interphalangeal arthrodesis along with tendon reconstruction at the MCP joint. 