Occipital condylar fractures - classification by Anderson and Montesano

The Anderson and Montesano classification was published in 1988. It divides occipital condylar fractures into three types according to their morphology and mechanisms of injury.

Type Description Mechanism Note
Type I comminuted fracture without or with minimal displacement of fragments axial load the ipsilateral alar ligament may be injured, stability is preserved by the contralateral alar ligament and the tectorial membrane, bilateral lesions may be unstable
Type II linear fracture as a part of a basioccipital fracture, fracture line extends from the foramen magnum to the skull base extension stability is preserved by intact alar ligaments and tectorial membrane
Type III avulsion fracture of the condyle near the alar ligament rotation and lateroflexion injury to the tectorial membrane and the contalateral alar ligament may cause instability


1. Anderson PA, Montesano PX. Morphology and treatment of occipital condyle fractures. Spine. 1988 Jul;13(7):731–6.
2. Leone A, Cerase A, Colosimo C, Lauro L, Puca A, Marano P. Occipital Condylar Fractures: A Review1. Radiology. 2000 Sep 1;216(3):635–44.
3. Malham GM, Ackland HM, Jones R, Williamson OD, Varma DK. Occipital condyle fractures: incidence and clinical follow-up at a level 1 trauma centre. Emerg Radiol. 2009 Jul 1;16(4):291–7