Axis fractures: historical systems and advancements with the AO spine classification.

STUDY

DESIGN

Systematic Review.

BACKGROUND

A variety of C2 (axis) and C2/3 historical classification systems have been proposed but there still remains a need for a rational hierarchical means of characterizing these traumatic spinal injuries which involve the axis. We evaluate the utility of existing classification systems and discuss the evolution of the validated AO Spine Upper Cervical Injury Classification (UCIC) System.

METHODS

A comprehensive search of MEDLINE, EMBASE and Cochrane Databases was performed in keeping with the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines to identify all published axis and traumatic C2/3 injury classification systems.

RESULTS

896 articles were distilled to 14 publications which proposed novel axis or traumatic C2/3 spondylolisthesis classification systems. The AO Spine Upper Cervical Spine Injury Classification System distils these into 3 types. Type A injuries are purely bony without tension band or disc involvement, derived from the three classical types of Anderson and D'Alonzo bony injuries. This includes later supplementary modifications proposed by Hadley as the type 2A fracture and Grauer who clarified a distinction between type 2 and 3 based upon superior articular facet involvement. Type B injuries include tension band or ligamentous injuries with or without bony injury whilst Type C injuries include any injury that leads to translation or traumatic spondylolisthesis of C2 on C3. This category would incorporate Effendi injuries types 2 and 3, Levine and Edwards types 2 and 3 as well as the atypical version proposed by Starr and Eismont. This category would also include Francis et al types 3,4 and 5 injuries. All of these injuries were proposed by their respective authors as unstable, and have now been easily condensed into the single type C category by the novel AO upper cervical spine classification system.

CONCLUSIONS

The mobility afforded at the axis and C2/3 articulation results in multiple fracture patterns each with a unique disruption of bony and ligamentous structures. This has led to the development of a multitude of bewildering historical systems. The AO Spine UCIC System represents a synthesis of existing historical knowledge and evolution into a universal clinically applicable validated system.