Courtesy: Gustavo Gomez Rodriguez, Buenos Aires, Argentina

 

Scaphoid Nonunion: Principles of Management

Overview

• Scaphoid nonunion occurs because of:
  • Fragment instability
  • Poor blood supply to proximal pole
  • Large cartilage-covered surface
  • Exposure to synovial fluid
• Successful treatment requires:
  • Fracture union
  • Restoration of normal scaphoid anatomy
  • Correction of deformity
• Failure to restore anatomy can lead to:
  • Abnormal wrist mechanics
  • Progressive arthritis
  • Carpal collapse

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Normal Wrist Biomechanics

Under Axial Loading

• Scaphoid tends to flex
• Triquetrum tends to extend
• Distal carpal row pronates in coordinated motion

After fracture:

• Distal fragment:
  • Flexes
  • Pronates with distal carpal row
• Proximal fragment:
  • Extends with proximal carpal row

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Pathomechanics of Scaphoid Nonunion

Distal Fragment

• Flexion + pronation
• Impinges against radial styloid

Proximal Fragment

• Extends dorsally

Result:

• Increased intrascaphoid angle
• Reduced scaphoid height
• Humpback deformity
• DISI deformity
• Progressive carpal malalignment

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Causes of Nonunion

• Fragment displacement
• Poor proximal pole vascularity
• Synovial fluid exposure
• Persistent instability

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Degenerative Progression

Early Arthritis

• Between distal scaphoid fragment and radial styloid

Later Progression

• Midcarpal degeneration
• Advanced radiocarpal arthritis

This progression is called:

• Scaphoid Nonunion Advanced Collapse (SNAC wrist)

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Evaluation

CT Scan – Most Important Investigation

CT assesses:

• Site of nonunion
• Degree of deformity
• Intrascaphoid angle
• Scaphoid height
• Bone quality
• Trabecular pattern
• Progress of healing

Goal of imaging:

• Assess both union and restoration of anatomy

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Main Treatment Goals

• Achieve bony union
• Restore scaphoid length
• Restore scaphoid height
• Correct humpback deformity
• Reduce intrascaphoid angle
• Restore carpal congruity and alignment

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Treatment Options

1. Fixation Alone

• Selected nonunions with:
  • Good biology
  • Minimal deformity

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2. Nonstructural Cancellous Bone Graft

• Supports union
• Used when major deformity correction is not needed

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3. Structural Corticocancellous Bone Graft

Preferred When Deformity Exists

Advantages:

• Restores scaphoid shape
• Corrects humpback deformity
• Provides mechanical support

Graft sources:

• Iliac crest
• Distal radius

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Distal Radius Structural Graft Technique

Advantages:

• Same operative field
• Less donor-site morbidity

Key steps:

1. Expose nonunion
2. Remove sclerotic bone
3. Reach healthy bleeding bone
4. Correct deformity
5. Pack cancellous graft
6. Insert structural graft volarly
7. Fix with compression screw

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Importance of Deformity Correction

• Union alone is insufficient if malalignment persists
• Restoration of scaphoid height is critical
• Midcarpal congruity must be reassessed after fixation

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Vascularized Bone Grafting

Indications

Used in:

• Poor biology
• Recalcitrant nonunion
• Proximal pole nonunion with vascular compromise

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Common Vascularized Graft

1,2 Intercompartmental Supraretinacular Artery Graft

• Pedicled dorsal distal radius graft

Fixation:

• Screw fixation
• K-wire fixation

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Role of Vascularized Grafts

Potential advantages:

• Improved biology
• Faster healing

Important point:

• Not proven superior in all studies
• Not every proximal pole nonunion requires vascularized grafting

Reserved mainly for:

• Difficult nonunions
• Revision cases
• Compromised vascularity

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Follow-Up

Assess:

• Maintenance of reduction
• Scaphoid height
• Intrascaphoid angle
• Graft position
• Progress toward union

CT is particularly useful during early healing.

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Practical Surgical Points

• Compression screw fixation commonly used
• Additional K-wire support may improve rotational stability
• Accurate reduction is as important as union
• Malunion can produce major functional problems

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Complications

• Persistent nonunion
• Malunion
• Loss of correction
• Progressive carpal collapse
• Degenerative arthritis
• Wrist pain and stiffness

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Key Exam Pearls

• Scaphoid nonunion occurs due to:
  • Instability
  • Poor proximal pole blood supply
  • Synovial environment
• Humpback deformity:
  • Increased intrascaphoid angle
  • Reduced scaphoid height
• CT scan is the best investigation for:
  • Planning
  • Follow-up
• Structural graft preferred when deformity correction is required
• Vascularized grafts usually reserved for:
  • Difficult
  • Recurrent
  • Biologically compromised nonunions