What is the treatment for a dislocated metacarpophalangeal (MP) joint of the thumb?

Treatment of Dislocated Metacarpophalangeal (MP) Joint of the Thumb

Dislocated MP joints of the thumb require prompt reduction, with surgical intervention necessary for complex dislocations that cannot be reduced by closed methods.

Classification and Initial Assessment

• Thumb MP dislocations can be categorized into three types: Type A (stable joint without severe ligament injury), Type B (palmar displaced extensor tendons preventing reduction), and Type C (joint instability due to severe collateral ligament disruption) 1
• Radiographic assessment with at least 2 views (PA and lateral) is essential to evaluate fracture displacement and articular involvement 2
• Assessment should determine if the dislocation is simple (reducible by closed methods) or complex (irreducible, requiring surgical intervention) 1, 3

Treatment Algorithm

Closed Reduction (Simple Dislocations)

• Attempt closed reduction for Type A dislocations (stable joint without severe ligament injury) 1
• Apply gentle traction followed by manipulation to reduce the joint 3
• After successful reduction, immobilize with a thumb spica cast or splint for 3-6 weeks 2
• Obtain follow-up radiographs at 10-14 days to ensure maintained reduction 2

Surgical Management (Complex Dislocations)

• Surgical intervention is indicated when:

  • Closed reduction fails (particularly Type B dislocations with interposed extensor tendons) 1, 3
  • Joint instability exists due to severe ligamentous injuries (Type C) 1
  • Fracture fragment displacement >3mm is present 2
  • More than one-third of the articular surface is involved 2

• Surgical approach options:

  • Dorsal approach: Simpler and safer but requires longitudinal division of the volar plate with theoretical risk of late instability 4
  • Palmar approach: Allows restoration of normal anatomy but places the radial neurovascular bundle at risk 4, 5
  • The choice between approaches depends on the specific mechanism of dislocation 5

• Surgical procedure involves:

  • Open reduction of the dislocation 1, 3
  • Repair of damaged ligaments, particularly the volar plate 1, 5
  • For open dislocations: thorough cleansing of the wound, primary wound closure, and antibiotic prophylaxis 6

Post-Treatment Management

• Immobilization with thumb spica cast or splint for 3-6 weeks following reduction 2
• Early range-of-motion exercises are recommended after the immobilization period for complete rehabilitation 5
• Follow-up should monitor pain relief and restoration of function 2

Prognosis and Complications

• Patients with complex dislocations requiring surgical intervention may experience decreased range of motion despite successful treatment 1
• Open dislocations have risk of infection but can achieve excellent range of motion with proper treatment 6
• Sound repair of ligamentous structures is important for long-term joint stability 5

Important Considerations

• The volar plate is often the most significant barrier to reduction in complex dislocations 4, 3
• For thumb base osteoarthritis, orthoses should be considered for symptom relief with long-term use advocated 7
• Surgery (e.g., interposition arthroplasty, osteotomy, arthrodesis) should be considered for severe thumb base OA when conservative treatments have failed 7