Is an odontoid process fracture in the cervical spine considered unstable?

Odontoid Process Fractures: Instability Assessment and Management

Odontoid process fractures in the cervical spine are considered unstable, particularly Type II fractures which occur at the base of the odontoid between the transverse ligament and C2 vertebral body. These fractures represent one of the most common and potentially dangerous cervical spine injuries, with significant risk for neurological compromise if not properly managed 1.

Classification and Instability Assessment

Type II odontoid fractures are inherently unstable due to their location and biomechanics:

• Type II fractures (most common type) occur at the junction of the odontoid process and the body of the axis, considered relatively unstable 2
• Fracture line direction influences stability:
  • Horizontal, downward and backward, or comminuted fracture lines indicate instability 3
  • Downward and forward fracture lines may be more stable 3
• Displacement is a critical factor:
  • Displacement >7mm indicates severe instability requiring more aggressive intervention 3
  • Associated Jefferson fracture (C1) significantly increases instability 3

Risks of Missed Diagnosis

Proper identification and management is critical because:

• Missed or delayed diagnosis increases secondary neurological injury rates by 10-fold 1
• Up to 67% of patients with missed fractures suffer neurological deterioration 1
• 29.4% of cases with delayed diagnosis develop permanent neurological deficits 1

Imaging Recommendations

The American College of Radiology recommends:

• CT is the gold standard for identifying cervical spine fractures, significantly outperforming radiographs which identify only about one-third of fractures visible on CT 4, 1
• MRI is complementary to assess:
  • Discoligamentous complex integrity
  • Associated soft-tissue injuries
  • Potential instability not apparent on CT 4, 1

Treatment Approach

Treatment should be based on fracture characteristics and patient factors:

Conservative Management

• External immobilization with hard cervical collar or cervicothoracic orthosis for stable fractures 5
• Halo vest immobilization is associated with high complication rates in elderly patients 2, 5

Surgical Indications

• Unstable fractures (horizontal, downward and backward, or comminuted fracture lines) 3
• Displacement >7mm 3
• Associated Jefferson fracture 3
• Neurological deficit 2
• Polytrauma 2
• Elderly patients (even with stable fractures) may have better outcomes with surgical treatment 5

Surgical Options

1. Anterior odontoid screw fixation for:

   • Reducible fractures with ideal fracture patterns
   • Displacement <7mm 3
   • Older patients may require fixation with 2 screws 5

2. Posterior C1-C2 instrumentation with fusion for:

   • Fractures with displacement >7mm
   • Associated Jefferson fracture
   • Inveterate fractures with severe C1-C2 dislocation 3

Conclusion

The evidence clearly demonstrates that odontoid process fractures, particularly Type II, should be considered unstable injuries requiring careful assessment and appropriate management to prevent the significant risk of neurological deterioration and permanent disability 1, 3, 2.