Updated: 10/9/2018

Thumb CMC Dislocation

Review Topic
  • Thumb CMC dislocation is mostly dorsal  
    • volar dislocation is rare  
  • Epidemiology
    • incidence
      • makes up <1% of hand injuries
  • Pathophysiology
    • mechanism
      • axial force on a flexed thumb (more common)
      • dorsal force applied in 1st web space (e.g. handlebar driven into a motorcyclist’s thumb on impact) (less common)
    • pathoanatomy
      • dorsoradial ligament is torn 
      • anterior oblique ligament is stripped/peeled off the 1st metacarpal base but remains continuous 
  • dorsal side ligaments are the primary stabilizers to dorsal/dorsoradial forces
  • 16 total ligaments that stabilize the TMC joint
    • superficial anterior oblique
      • does NOT stabilize joint in flexion
      • does NOT prevent dorsal subluxation
      • provides for laxity of TMCJ to allow pronation during opposition
      • forms “voluminous pouch” to accommodate metacarpal translation
    • deep anterior oblique (beak) ligament
      • pivot for TMCJ for pronation of thumb
    • dorsoradial ligament
      • stabilizer (“check rein”) to radial subluxation
        • becomes taut with radial/dorsoradial subluxation before other ligaments
        • if all other ligaments but this one are cut, CMC still remains reduced
      • lax in stage IV arthritis
    • posterior oblique ligament
    • ulnar collateral ligament
    • intermetacarpal ligament
    • dorsal intermetacarpal
    • dorsal trapeziotrapeziod
    • volar trapeziotrapeziod
    • dorso trapezio-II metacarpal
    • volar trapezio-II metacarpal
    • trapezio-III metacarpal
    • transverse carpal ligament
    • trapeziocapitate
    • volar scaphotrapezial
    • radial scaphotrapezial
  • 7 main stabilizers of TMCJ – SAOL, dAOL, DRL, POL, UCL, IML and DIML
  • 9 stabilizers of trapezium – DTT, VTT, DT-II MC, VT-II MC, T-III MC, VST, RST, trapeziocapitate and transverse carpal
  • 4 key ligamentous restraints of the thumb
    • anterior oblique ligament
      • remains attached to volar fragment in Bennett/Rolando fracture
    • posterior oblique ligament
    • intermetacarpal ligament
    • dorsoradial ligament
  • History 
    • collide onto fixed object/axial force on a flexed thumb 
    • dorsal force applied to 1st web space 
      • e.g. handlebar driven into a motorcyclist’s thumb on impact)
  • Symptoms
    • pain over thenar eminence
  • Physical exam
    • swelling, bruising over thenar eminence
    • unable to form a fist
  • Radiographs
    • recommended views
      • PA
      • lateral
    • optional views
      • roberts
        • used to evaluate for base of thumb fractures
    • findings
      • joint space widening
      • dorsoradial shift of metacarpal
  • MRI 
    • indications
      • persistent/recurrent instability after reduction
      • guide to ligamentous reconstruction
  • Nonoperative
    • closed reduction and immobilization in extension and pronation
      • indications
        • stable on reduction (implying the AOL is intact)
  • Operative
    • closed reduction and temporary pinning
    • reconstruction of the dorsal capsuloligamentous complex with tendon autograft + temporary pinning
      • recommended treatment
      • indications
        • grossly unstable joint (AOL possibly torn as well)
      • results
        • better abduction and pinch strength than closed reduction and pinning
  • Anterior osteophyte often visible
  • Low incidence of recurrent dislocation 

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