Anderson and Montesano classification of occipital condyle fractures

Last revised by Assoc Prof Craig Hacking on 13 Apr 2021

The Anderson and Montesano classification of occipital condyle fractures is the most widely used scheme for describing occipital condyle fractures and divides injuries into three types based on morphology and mechanism of injury 1,2,3.

Classification

  • type I - comminuted (3-15%)
    • impaction fracture of occipital condyle
    • associated with axial compression injury
    • stable injury
  • type II - basilar skull (25-50%)
    • basilar skull fracture extending into the occipital condyle
    • associated with a direct blow to the lower skull
    • stable injury
  • type III - avulsion (35-75%)
    • condylar avulsion injury at the alar ligament attachment
    • associated with forced contralateral bending and rotation
    • potentially unstable injury

Since the Anderson and Montesano system is purely descriptive, a more clinically-oriented classification has been proposed by Tuli et al 5. The latter incorporates MRI findings, and is tiered according to suggested management 2,4:

  • type I - non-displaced fracture - may not require stabilization
  • type II - displaced fracture
    • IIA - no ligamentous instability, may require external stabilization
    • IIB - ligamentous instability, may require surgical fixation

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Cases and figures

  • Figure 1: type 1
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  • Case 1: type 1
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  • Case 2: type 1
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  • Case 3: type 1
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  • Figure 2: type 2
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  • Case 4: type 2
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  • Case 5: bilateral type 2
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  • Figure 3: type 3
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  • Case 6: type 3
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  • Case 7: type 3
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  • Case 8: bilateral type 3
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