Update on Upper Cervical Injury Classifications: The New AO Upper Cervical Spine Classification System.

The upper cervical spine accounts for the largest proportion of cervical range of motion afforded by a complex system of bony morphology and ligamentous stability. Its unique anatomy, however, also makes it particularly vulnerable during both low and high energy trauma. Trauma to this area, referred to as upper cervical spine trauma, can disrupt the stability of the upper cervical spine and result in a wide spectrum of injury. Numerous upper cervical injury classification systems have been proposed, each of which have distinct limitations and drawbacks that have prevented their universal adoption. In this article, we provide an overview of previous classifications, with an emphasis on the development of the new AO Spine Upper Cervical Classification System (AO Spine UCCS).