title: Os odontoideum revisited: the case for a multifactorial etiology.
abstract: METHODS
  Retrospective analysis of our experience with os odontoideum at the Children's Hospital of Philadelphia.
  
  
  OBJECTIVE
  To review the origin of os odontoideum and provide evidence for two separate etiologies.
  
  
  BACKGROUND
  The etiology of os odontoideum has been debated in the literature. Most authors support a post-traumatic etiology; however, some evidence exists to support a congenital origin.
  
  
  METHODS
  We reviewed all 519 abnormal cervical spine radiographs performed from 1991 to 2004 to identify os odontoideum. Medical records and imaging studies were examined to determine: history of trauma, severity of injury, interval from injury to presentation, coexisting syndromes, and associated congenital cervical spine anomalies.
  
  
  RESULTS
  Sixteen of 519 patients (3.1%) had os odontoideum. Only 8 of 16 patients reported previous trauma. Only 3 of these 8 injuries occurred with an interval remote enough to allow remodeling of the dens to an ossicle by the time of presentation. Six of 16 patients had associated congenital anomalies in the cervical spine. Three of 16 had a coexisting genetic syndrome.
  
  
  CONCLUSIONS
  Our data supports two separate etiologies for the os odontoideum: post-traumatic and congenital. The data should raise awareness that some children with preexisting syndromes may develop os odontoideum without previous trauma.
authors.affiliation: Division of Orthopaedic Surgery, Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA.
authors.forename: Wudbhav N
authors.initials: WN
authors.lastname: Sankar
authors.forename: Brian P D
authors.initials: BP
authors.lastname: Wills
authors.forename: John P
authors.initials: JP
authors.lastname: Dormans
authors.forename: Denis S
authors.initials: DS
authors.lastname: Drummond
mesh_terms: D000293:Adolescent; D001268:Atlanto-Axial Joint / Q000000981:diagnostic imaging; D015984:Causality; D002574:Cervical Vertebrae / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000293:injuries*; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008297:Male; D009809:Odontoid Process / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000293:injuries*; D015143:Philadelphia / Q000453:epidemiology; D012189:Retrospective Studies; D013122:Spinal Diseases / Q000151:congenital / Q000453:epidemiology / Q000473:pathology; D014057:Tomography, X-Ray Computed