The Anderson and Montesano classification is a widely used system for describing occipital condyle fractures. It divides injuries into three types based on morphology and mechanism of injury ^1-5.

Classification

• type I: impacted type occipital condyle fracture
  • morphology: comminution of the condyle with minimal or no displacement of fragments into the foramen magnum
  • mechanism: axial loading of the skull onto the atlas
  • stability: stable because the tectorial membrane and contralateral alar ligament are intact (the ipsilateral alar ligament may be functionally inadequate)
• type II: basilar skull type occipital condyle fracture
  • morphology: condyle fracture that extends outside of the condyle to elsewhere in the posterior base of skull
  • mechanism: direct blow to the lower skull
  • stability: stable because the tectorial membrane and alar ligaments are intact
• type III: avulsion type occipital condyle fracture
  • morphology: small inferomedial occipital condyle fracture fragment displaced toward the odontoid tip
  • mechanism: rotation and/or contralateral bending
  • stability: potentially unstable due to loading of the contralateral alar ligament and tectorial membrane

Epidemiology

A range of incidences of the Anderson and Montesano types amongst all occipital condyle fractures has been reported ^2,4,6:

• type I: 3-13%
• type II: 22-54%
• type III: 33-75%

History and etymology

The classification was described in 1988 by American orthopaedic surgeons Paul A. Anderson and Pasquale X. Montesano on the basis of 6 patients diagnosed by conventional anterior posterior polytomography or CT with coronal reconstructions ¹.

See also

• Tuli classification of occipital condyle fractures