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Updated: Aug 4 2022

Thumb CMC Dislocation

  • summary
    • Thumb CMC Dislocations are rare injuries that occur due to axial force on a flexed thumb.
    • Diagnosis is clinical and can be confirmed by orthogonal radiographs.
    • Treatment is closed reduction and immobilization with unstable injuries requiring surgical stabilization.
  • Epidemiology
    • Incidence
      • makes up <1% of hand injuries
    • Anatomic location
      • Mostly dorsal dislocations
        • Volar dislocations are rare
  • Etiology
    • 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
  • Anatomy
    • 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
  • Presentation
    • 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
  • Imaging
    • 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
  • Diagnosis
    • Radiographic
      • diagnosis confirmed by history, physical exam, and radiographs
  • Treatment
    • 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
  • Complications
    • Anterior osteophyte often visible
    • Low incidence of recurrent dislocation
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