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  • A Zone III extensor tendon injury characterized by  
    • PIP flexion
    • DIP extension
  • Mechanism
    • caused by rupture of the central slip over PIP joint from
      • laceration
      • traumatic avulsion (jammed finger)
      • capsular distension in rheumatoid arthritis
  • Pathoanatomy
    • pathoanatomic sequence includes
      • rupture of central slip 
        • causes the extrinsic extension mechanism from the EDC to be lost
        • prevents extension at the PIP joint
      • attenuation of triangular ligament 
        • causes intrinsic muscles of the hand (lumbricals) to act as flexors at the PIP joint
        • lumbricals also extend the DIP joint without an opposing or balancing force
      • palmar migration of collateral bands and lateral bands
        • the lumbricals' pull becomes unopposed, pulling through the base of the distal phalanx and volar to the PIP
        • causes PIP flexion and DIP extension
    • bone deformity
      • injury involves all three phalanges
      • the middle phalanx flexes on the proximal phalanx at the PIP joint
      • the distal phalanx is hyperextended relative to the middle phalanx at the DIP joint
  • Associated conditions
    • rheumatoid arthritis
    • pseudo-boutonniere
      • refers to PIP joint flexion contracture in the absence of DIP extension
  • Muscle
    • lumbrical muscles
      • originate from the FDP and insert on the lateral bands
  • Ligament anatomy
    • extensor hood and central slip
      • the extrinsic extensor tendon joins the extensor hood at the MCP
      • the central portion of the extensor hood forms the central slip
      • the central slip inserts onto the middle phalanx and acts to extend the PIP joint
    • lateral bands
      • the lateral bands are formed from the deep head of the dorsal interossi combining with the volar interossi
      • the lateral bands insert onto the base of the distal phalanx to extend the DIP joint
    •  triangular ligament
      • spans the two lateral bands, preventing them from subluxing volarly
    • transverse retinacular ligament
      • prevents dorsal subluxation of the lateral bands
  • Blood supply
    • interosseous muscles
      • receive blood from vessels formed by a combination of the deep palmer arch and the ulnar artery
  • Physical exam 
    • deformity
      • characterized by PIP flexion DIP extension 
    • Elson test  
      • is the most reliable way to diagnose a central slip injury before the deformity is evident
      • bend PIP 90° over edge of a table and extend middle phalanx against resistance.
        • in presence of central slip injury there will be
          • weak PIP extension
          • the DIP will go rigid
        • in absence of central slip injury DIP remains floppy because the extension force is now placed entirely on maintaining extension of the PIP joint; the lateral bands are not activated
  • Radiographs
    • recommended view
      • radiographs are not required in evaluation and treatment of Boutonniere deformity
  • Nonoperative
    • splint PIP joint in full extension for 6 weeks
      • indications
        • acute closed injuries (< 4 weeks)
      • technique
        • encourage active DIP extension and flexion in splint to avoid contraction of oblique retinacular ligament
        • complete part-time splinting for an additional 4-6 weeks
  • Operative
    • primary central band repair
      • indications
        • acute displaced avulsion fx (proximal MP avulsion seen on x-ray)
        • open wound that needs I&D
    •  lateral band relocation vs. terminal tendon tenotomy vs. tendon reconstruction 
      • indications
        • in chronic injuries after FROM is obtained with therapy or surgical release
      • technique
        • terminal tendon tenotomy (modified Fowler or Dolphin tenotomy)(never central slip tenotomy)
        • secondary tendon reconstruction (tendon graft, Littler, Matev)
        • triangular ligament reconstruction
    • PIP arthrodesis
      • indications
        • rheumatoid patients
        • painful, stiff and arthritic PIP joint

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