title: Congenital anterior midline cleft of the atlas and posterior atlanto-occipital fusion associated with symptomatic anterior atlantoaxial subluxation.
abstract: BACKGROUND
  Congenital partial anterior arch defect of the atlas is extremely rare. It could be found as an incidental radiological finding or patients can present with neurological deficit after head or neck trauma.
  
  
  OBJECTIVE
  To describe an extremely rare presentation of anterior midline cleft at the atlas and congenital posterior atlanto-occipital fusion with symptomatic anterior atlantoaxial subluxation. This report includes a feasible hypothesis for the development of this anomaly on the basis of previous hypotheses and surgical findings.
  
  
  METHODS
  A 46-year-old female presented with a 6-day history of right limbs numb and left upper and lower extremities paraparesis (Frankel D). Radiographs of the cervical spine showed anterior atlantoaxial subluxation with congenital posterior atlanto-occipital fusion. Computed tomography subsequently revealed partial midline absence of the anterior arch of the atlas and the odontoid tip ahead of the anterior arch of the atlas. Magnetic resonance imaging showed that the cervical dura was compressed by the remnant of anterior arch of the atlas. The patient underwent Gardner-Wells tong traction and surgery of occipitocervical fusion with autogenous iliac bone graft because she had definite neurological symptom and congenital posterior atlanto-occipital fusion.
  
  
  RESULTS
  Atlantoaxial reduction was confirmed with fluoroscopic X-ray evaluation by bed, her neurological deficit was resolved from Frankel D to E, and numb of right limbs completely disappeared 6 days postoperation. No instability has been observed during 2-year follow-up.
  
  
  CONCLUSIONS
  We describe the association between compressive myelopathy and congenital defect of the anterior arch of the atlas with symptomatic anterior atlantoaxial subluxation. Both computed tomography and magnetic resonance image were required to demonstrate the bony configuration and cord compression. And Gardner-Wells tong traction and surgery of occipitocervical fusion with autogenous iliac bone graft were effective as a treatment for this compressive myelopathy caused by the remnant of anterior arch of the atlas.
authors.affiliation: Department of Orthopedic, Southwest Hospital, Third Military Medical University, No. 30 Gaotanyan Street, Chongqing, 400038, People's Republic of China.
authors.forename: Qingyi
authors.initials: Q
authors.lastname: He
authors.affiliation: Department of Orthopedic, Southwest Hospital, Third Military Medical University, No. 30 Gaotanyan Street, Chongqing, 400038, People's Republic of China. jianzhongxu@yeah.net.
authors.forename: Jianzhong
authors.initials: J
authors.lastname: Xu
keywords: Anterior arch; Atlas; Congenital cleft; Neurological deficit