Methods: A systematic literature review and consensus using the Delphi method. Objective: The aim was to formulate consensus recommendations regarding the natural history, diagnosis, classification, and optimal treatment of os odontoideum with global applicability.

Background: Os odontoideum (OO) is a rare anomaly of the cranio-vertebral junction (CVJ). Due to the paucity of literature, there is still considerable debate about the clinical management of OO.

Methods: Using PubMed, the authors reviewed the literature on OO published from 2011 to 2022. Using the Delphi method, a panel of expert spine surgeons and members of the WFNS Spine Committee analyzed the strength of the published literature and elaborated and voted on statements concerning diagnosis and management.

Results: The diagnosis may be established incidentally. Symptoms may manifest as neck discomfort or encompass occipital-cervical pain, myelopathy, or vertebrobasilar ischemia. Diagnosis is usually made with plain radiographs and CT scans. Dynamic x-rays identify C1-C2 instability, whereas MRI assesses spinal cord integrity and compression. Asymptomatic cases lacking radiologic instability are generally handled through regular observation and serial imaging until predictors of neurological deterioration necessitate surgical intervention. In the event of atlantoaxial instability or neurological dysfunction, surgical intervention with instrumentation and fusion is required to maintain stability. In irreducible cases, C1-2 joint manipulation and distraction permits realignment and deformity correction avoiding decompression, either from anterior or posterior.

Conclusions: The management guidelines for asymptomatic OO are still a gray zone as our understanding of the natural history is still vague. Therefore, we need more large-center studies to investigate this condition further. Whenever symptomatic, unstable, or asymptomatic presenting with risk factors, OO is better managed with atlantoaxial fusion, avoiding occipital inclusion in the construct. In irreducible OO, C1-C2 joint manipulation and distraction are preferred to decompression.