Boutonniere deformity is characterized by which pattern of joint involvement?

Boutonniere deformity is characterized by which pattern of joint involvement?

• A. Hyperextension of PIP with flexion of DIP
• B. Persistent flexion of the PIP joint with hyperextension of the DIP joint
• C. Extension of MCP joints
• D. Hyperextension of the wrist

Answer: (B)

Boutonniere deformity reflects a disruption of the extensor mechanism at the PIP joint, specifically the central slip. When the central slip is injured, the PIP loses the ability to extend and tends to sit in flexion. The lateral bands slide volarly and pull the middle phalanx into flexion, while the intact extensor mechanism at the distal phalanx continues to extend the DIP, causing the DIP to lie in hyperextension. So the characteristic pattern is that the PIP remains flexed while the DIP is hyperextended. This helps distinguish it from other finger deformities like swan neck, where the PIP is hyperextended and the DIP is flexed. The other patterns don’t match the way the extensor mechanism distributes force after central slip injury.

Boutonniere deformity reflects a disruption of the extensor mechanism at the PIP joint, specifically the central slip. When the central slip is injured, the PIP loses the ability to extend and tends to sit in flexion. The lateral bands slide volarly and pull the middle phalanx into flexion, while the intact extensor mechanism at the distal phalanx continues to extend the DIP, causing the DIP to lie in hyperextension. So the characteristic pattern is that the PIP remains flexed while the DIP is hyperextended. This helps distinguish it from other finger deformities like swan neck, where the PIP is hyperextended and the DIP is flexed. The other patterns don’t match the way the extensor mechanism distributes force after central slip injury.