What is an acceptable angle of displacement for a boxer fracture?

Acceptable Angle of Displacement for Boxer's Fracture

For boxer's fractures (fifth metacarpal neck fractures), an acceptable angle of displacement is up to 30 degrees of volar angulation, as this preserves 92% of grip strength and 78% of range of motion. Beyond this angle, functional impairment becomes more significant and surgical intervention may be warranted.

Biomechanical Considerations

• Biomechanical studies have demonstrated that as fracture angulation increases beyond 30 degrees, there is progressive shortening of the intrinsic muscles (particularly the flexor digiti minimi) 1
• This muscle shortening creates "slack" that affects:
  • Initiation of metacarpophalangeal joint flexion
  • Overall grip strength
  • Range of motion

Management Algorithm Based on Angulation

Acceptable for Conservative Management (≤30°)

• Fractures with volar angulation ≤30° can be managed conservatively with excellent functional outcomes
• Conservative management options include:
  • Functional treatment with pressure bandage for 1 week followed by immediate mobilization 2
  • Ulnar gutter splint or cast for 3-4 weeks

Borderline Cases (30-50°)

• Some institutions use pathways that accept up to 50° of palmar angulation for uncomplicated fractures 3
• These patients generally have good functional outcomes and can return to work immediately
• However, this exceeds the biomechanically optimal threshold of 30°

Requires Reduction (>50-70°)

• Fractures with angulation >50° typically require closed reduction
• After reduction, external immobilization with combination of malleable aluminum alloy splint and plaster cast can maintain the reduction 4
• Some studies suggest that even angulations up to 70° may be acceptable if treated with immediate mobilization 2, but this contradicts biomechanical evidence

Surgical Intervention (>70° or Other Complications)

• Fractures with angulation >70°
• Fractures with rotational deformity (any degree)
• Open fractures
• Intra-articular extension
• Failed closed reduction

Important Clinical Considerations

• Always assess for rotational deformity, which is not acceptable at any degree
• Check for digital overlap during flexion, which indicates malrotation
• Early mobilization (within pain limits) produces better functional outcomes than prolonged immobilization
• Patient-specific factors to consider:
  • Dominant vs. non-dominant hand
  • Occupational demands
  • Athletic requirements
  • Age and healing potential

Imaging Assessment

• Standard 3-view radiographic examination (PA, lateral, and oblique) is typically sufficient for diagnosis and measuring angulation 5
• An internally rotated oblique projection can increase diagnostic yield for accurate measurement of angulation

Pitfalls to Avoid

• Failing to assess for rotational deformity, which requires correction regardless of angulation
• Attempting aggressive reduction of fractures with <30° angulation, which provides no functional benefit
• Prolonged immobilization, which can lead to stiffness and delayed return to function
• Overlooking patient-specific functional requirements when deciding on acceptable angulation

The biomechanical evidence strongly supports 30° as the upper limit for acceptable final angulation in boxer's fractures, as this preserves nearly normal hand mechanics while allowing for successful conservative management 1.