Updated: 10/4/2016

Swan Neck Deformity

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Introduction
  • Characterized by
    • hyperextension of PIP
    • flexion of DIP
  • Caused by
    • lax volar plate
    • imbalance of muscle forces on PIP (extension force > flexion force)
  • Injuries include
    • MCP joint volar subluxation (rheumatoid arthritis)
    • mallet finger
    • FDS laceration
    • intrinsic contracture
  • Seen in rheumatoid arthritis
Pathoanatomy
  • Primary lesion is lax volar plate that allows hyperextension of PIP. Causes include
    • trauma
    • generalized ligament laxity
    • rheumatoid arthritis
  • Secondary lesion is imbalance of forces on the PIP joint (PIP extension forces that is greater than the PIP flexion force). Causes of this include
    • mallet injury
      • leads to transfer of DIP extension force into PIP extension forces
    • FDS rupture
      • leads to unopposed PIP extension combined with loss of integrity of the volar plate
    • intrinsic contracture
      • tethering of the lateral (collateral) bands by the transverse retinacular ligament as a result of PIP hyperextension.
      • if the lateral (collateral) bands are tethered, excursion is restricted and the extension force is not transmitted to the terminal tendon, and is instead transmitted to the PIP joint
    • MCP joint volar subluxation
      • caused by rheumatoid arthritis
Presentation
  • Symptoms
    • snapping and locking of the fingers
  • Physical exam
    • hyperextension of PIP post
    • flexion of DIP
Imaging
  • Radiographs
    • recommended views 
      • AP and lateral view of the affected hand
Treatment
  • Nonoperative
    • double ring splint
      • indications
        • can prevent hyperextension of PIP
  • Operative
    • volar plate advancement and PIP balancing with central slip tenotomy
      • indications
        • progressive deformity
      • technique
        • address volar plate laxity with volar plate advancement
        • correct PIP joint muscles imbalances with either
          • FDS tenodesis indicated with FDS rupture
          • spiral oblique retinacular ligament reconstruction
          • central slip tenotomy (Fowler)
 

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