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Updated: May 14 2021

MCP Dislocations

  • Summary
    • MCP Dislocations are a dislocation of the metacarpophalangeal joint, usually dorsal, caused by a fall and hyperextension of the MCP joint.
    • Diagnosis can be made clinically and is confirmed by orthogonal radiographs.
    • Treatment is closed reduction unless soft tissue interposition blocks reduction, in which case open reduction is indicated.
  • Epidemiology
    • Incidence
      • rare
        • < 1 per 100,000 annually 
    • Anatomic location
      • dorsal dislocations are most common
      • index finger is most commonly involved
        • thumb is second most common digit involved
  • Etiology
    • Pathophysiology
      • mechanism of injury
        • usually a fall on outstretched hand leading to hyperextension of MCP joint
          • leads to avulsion of the volar plate from metacarpal neck
    • Associated conditions
      • metacarpal and phalanx fractures
        • fractures of the base of proximal phalanx or metacarpal head
          • seen in up to 50%
  • Anatomy
    • MCP Joint Osteology
      • a condyloid joint
        • proximal phalanx
          • contains shallow and concave surface
            • congruent with metacarpal head
        • metacarpal head
          • is cam shaped
      • sesamoids
        • embedded in the volar plate
        • attached to flexor pollicis brevis and abductor pollicis brevis in thumb
    • MCP Joint Ligaments
      • proper collateral ligaments
        • are the primary stabilizer of the MCP joint
        • originate from the dorsal aspect of metacarpal head
        • insert on the volar aspect of base of proximal phalanx
        • are tight in flexion
      • accessory collateral ligaments
        • originate volar to the proper collateral ligaments
        • insert on the volar plate
        • are tight in extension
      • volar plate
        • stabilizes the volar aspect of MCP joint
        • comprised of thick fibrocartilaginous portion distally and loose membranous portion proximally
          • allows for hyperextension of MCP joint
        • forms volar recess proximally
          • allows for flexion of proximal phalanx
      • dorsal capsule
        • a weak stabilizer of the dorsal aspect of MCP joint
        • thin and loose in structure
      • sagittal bands
        • supports the extrinsic tendons
        • originates from the extensor hood
        • attaches volarly with transverse metacarpal ligament
  • Classification
      • Anatomic classification of MCP dislocation
      • Volar
      • Results from hyperextension or hyperflexion injury
      • Dorsal
      • Most common
        Results from hyperextension injury
      • Complexity of MCP dislocation
      • Simple (subluxation)
      • No interposition of volar plate and/or sesamoid
        Base of proximal phalanx remains in contact with the metacarpal head
      • Complex (complete)
      • Interposition of volar plate and/or sesamoids
        Metacarpal head becomes entrapped by
      •     -displaced natatory ligaments distally
            -superficial transverse metacarpal ligament proximally
      • Kaplan's lesion (rare)
      •     -most common in index finger
            -metacarpal head buttonholes into palm (volarly)
            -volar plate is interposed between base of proximal phalanx and metacarpal head
  • Presentation
    • Physical exam
      • deformity seen on inspection depends on type of dislocation
        • dorsal dislocation
          • simple
            • hyperextension of proximal phalanx on metacarpal head
            • flexion of PIP joint
          • complex
            • bayonet positioning of proximal phalanx (dorsal to metacarpal shaft)
            • skin dimpling in proximal palmar crease
        • volar dislocation
          • extensor lag present
          • dorsal skin depression found proximal to base of proximal phalanx
  • Imaging
    • Radiographs
      • recommended views
        • AP
        • lateral
          • best view to see dislocation
        • oblique
      • findings
        • complex dislocation
          • joint space widening may indicate interposition of volar plate
          • entrapment of sesamoid in MCP joint is diagnostic of complex dislocation
  • Diagnosis
    • Radiographic
      • diagnosis confirmed by history, physical exam, and radiographs
  • Treatment
    • Nonoperative
      • closed reduction
        • indications
          • simple dislocations
    • Operative
      • open reduction
        • indications
          • complex dislocations/delayed presentation
  • Techniques
    • Closed Reduction
      • dorsal dislocation
        • reduction technique
          • apply direct pressure over dorsal aspect of proximal phalanx with the wrist in flexion to take tension off the intrinsic and extrinsic flexors
            • avoid longitudinal traction during closed reduction as it may pull volar plate into joint and convert to irreducible
        • immobilization
          • early ROM and dorsal blocking splint following successful reduction
      • volar dislocation
        • reduction technique
          • apply direct pressure over volar aspect of proximal phalanx with MCP in flexion
        • immobilization
          • immobilize in 30° of flexion for 2 weeks, then active ROM in dorsal blocking splint
    • Open reduction
      • approach
        • dorsal approach
          • approach
            • midline incision
          • soft tissue
            • split extensor tendon and joint capsule longitudinally
              • in thumb, develop interval between EPL and EPB
            • may be able to push volar plate out with freer elevator
              • usually need to split volar plate to remove from joint
          • pros
            • decreased risk of injury to neurovascular bundle
            • easier to address metacarpal head fractures
        • volar approach
          • approach
            • oblique incision
              • important to incise skin only to avoid injury to neurovascular bundle
          • soft tissue
            • release A1 pulley to expose volar plate
            • push volar plate and surrounding ligaments/tendons out with freer elevator
          • pros
            • provides better access to volar plate and surrounding ligaments/tendons
          • cons
            • risk of injury to neurovascular bundle
            • difficult to address osteochondral fractures
      • soft tissue reduction
        • identify and reduce soft tissue blocking reduction
          • dorsal dislocations
            • in thumb
              • FPL tendon displaces ulnarly to create a noose with radially displaced intrinsics
            • index finger
              • flexor tendon displaces ulnarly and lumbrical displaces radially which tighten around metacarpal neck
            • in small finger
              • flexor tendons and lumbrical displace radially and the abductor digiti minimi and flexor digiti minimi ulnarly
          • volar dislocations
            • interposition of dorsal capsule in joint
            • avulsion and entrapment of distal insertion of volar plate or collateral ligament
            • distal and volar displacement of tendinous juncture connecting 4th and 5th EDC tendons in small finger
            • entrapment of 1st dorsal interossei in thumb
  • Complications
    • Joint stiffness
      • due to soft tissue trauma at time of injury or prolonged immobilization
    • Post-traumatic arthritis or osteonecrosis
      • due to repeated attempts at closed reduction, prolonged dislocation, traumatic open reduction
    • Premature physeal closure
      • rare
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