Management of C2 fractures following multiple classifications, a narrative review

Introduction: Classifications are helpful for surgeons as they can be a resource for decision-making, often providing the individual indicators that may deem a case necessary for surgery. However, when there are multiple classifications, the decision-making might be compromised. That is the case with C2 fractures. For this reason, this study was designed to review the different classifications of axis fractures. Research question: What are the most commonly used classifications for C2 fractures, and how do these classifications compare in terms of clinical utility? Methods: A systematic literature review following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) Guidelines was performed. Three different Pub-med searches (https://pubmed.ncbi.nlm.nih.gov/) were done to isolate the most common C2 fracture classifications of odontoid process fractures, the posterior element of the axis and axis body fractures. Results: The search isolated 530 papers. Applying the inclusion and exclusion criteria yielded seven papers on axis body fractures, six on odontoid fractures, and ten on "hangman's fractures." Most of the classifications proposed are modified versions of the classic ones: Benzel's for body fractures, Anderson and D'Alonzo's for odontoid fractures, and Effendi's for "hangman's fractures." The proposal by AO Spine of a different classification seems promising and had good early results of interobserver and intraobserver agreement. Discussion and conclusion: Currently, no classification is universally accepted or widely used. The emergence of the AO Spine Upper Cervical Injury Classification system seems promising as it encompasses radiological and clinical elements.