## Hand Deformities in Rheumatoid Arthritis **Key Point:** Zigzag (or Z-deformity) is characterized by ulnar deviation of the fingers with volar subluxation of the metacarpophalangeal (MCP) joints, resulting from chronic synovitis and joint destruction. ### Classification of RA Hand Deformities | Deformity | Mechanism | MCP Position | PIP Position | DIP Position | Clinical Appearance | |-----------|-----------|--------------|--------------|--------------|---------------------| | **Zigzag** | Ulnar deviation + MCP volar subluxation | Subluxed volarly | Variable | Variable | Fingers deviate ulnarly with MCP sinking | | Swan-neck | MCP flexion + PIP hyperextension | Flexed | Hyperextended | Flexed | Graceful swan-like appearance | | Boutonnière | MCP extension + PIP flexion | Extended | Flexed | Extended | Buttonhole-like PIP flexion | | Z-thumb | CMC flexion + IP hyperextension | — | — | — | Thumb in Z shape | **High-Yield:** Zigzag deformity is one of the most characteristic and severe hand deformities in advanced RA, reflecting long-standing joint damage and synovial inflammation. **Clinical Pearl:** The presence of hand deformities in RA indicates: - Chronic, poorly controlled disease - Significant joint destruction on imaging - Need for aggressive DMARD therapy and possible hand surgery **Mnemonic:** **Z = Zigzag (Ulnar deviation + volar subluxation)** — think of the Z-shaped path the fingers take when deviated ulnarly and subluxed volarly. [cite:Robbins 10e Ch 19]
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