What is an avulsion fragment?

Avulsion Fractures: Definition and Clinical Significance

An avulsion fracture occurs when a small fragment of bone is pulled away from its main structure by an attached tendon or ligament during trauma, typically resulting from sudden forceful muscle contraction or extreme joint movement. 1

Characteristics of Avulsion Fractures

• Occur at sites where tendons or ligaments attach to bone
• Result from acute trauma, typically involving:
  • Twisting injuries
  • Sudden forceful muscle contractions
  • Direct trauma to the affected area

Common Locations

Avulsion fractures commonly occur in:

1. Ankle: Lateral talar process avulsions (often misdiagnosed as ankle sprains) 1
2. Knee:
   • Tibial plateau avulsions
   • Posterior cruciate ligament tibial attachment avulsions 2
   • Tibial tuberosity avulsions (rare in adults) 3
3. Hand/Wrist:
   • Bony avulsions at ligamentous attachments 1
   • Triangular fibrocartilage complex avulsions 4
4. Shoulder:
   • Coracoid process avulsions (can occur with recurrent dislocations) 5

Diagnostic Imaging

1. Initial Assessment: Radiography is the first-line imaging modality 1

   • Standard radiographic views (minimum 3 views) are essential
   • May show small bone fragments at tendon/ligament attachment sites

2. When Radiographs Are Negative or Equivocal:

   • MRI is the preferred next study for suspected occult avulsion fractures 1
   • CT may be used to better characterize fracture extent, displacement, and comminution 1

3. Special Considerations:

   • Stress radiographs may identify occult avulsion injuries at ligamentous attachments 1
   • Ultrasound can detect some superficial avulsion fractures and associated lipohemarthrosis 1

Clinical Significance

Avulsion fractures are important to identify because:

1. They indicate underlying soft tissue injury - The presence of an avulsion fragment often signals damage to the attached ligament or tendon 1

2. Treatment decisions depend on fragment characteristics:

   • Size of the avulsed fragment
   • Degree of displacement
   • Involvement of articular surface
   • Associated soft tissue injuries

3. Missed diagnosis can lead to:

   • Chronic instability
   • Functional impairment
   • Delayed healing

Treatment Considerations

Treatment depends on:

1. Fragment size and displacement:

   • Small, minimally displaced fragments: Often managed conservatively
   • Large fragments or those involving >1/3 of articular surface: May require surgical fixation 1

2. Location-specific considerations:

   • Osseous "mallet" injuries: Surgical fixation indicated when >1/3 of articular surface is involved 1
   • Palmar displacement >3mm or interfragmentary gap >3mm often requires surgery 1

3. Associated injuries:

   • Meniscal or ligamentous injuries may accompany avulsion fractures 1, 6
   • Detachment of soft tissue structures may require repair along with fragment fixation 2, 4

Pitfalls in Management

1. Misdiagnosis: Avulsion fractures (particularly lateral talar process) may be erroneously diagnosed as simple sprains 1

2. Delayed diagnosis: Can lead to functional impairment and chronic instability 1

3. Inadequate imaging: Single or dual-view radiographs are often insufficient; minimum 3 views are recommended 1

4. Overlooking associated injuries: Soft tissue injuries frequently accompany avulsion fractures and require appropriate treatment 1, 2