Clin Orthop Surg.  2014 Mar;6(1):96-100. 10.4055/cios.2014.6.1.96.

Congenital Anomaly of the Atlas Misdiagnosed as Posterior Arch Fracture of the Atlas and Atlantoaxial Subluxation

  • 1Department of Orthopedic Surgery, National Health Insurance Cooperation Ilsan Hospital, Goyang, Korea.


Partial or complete absence of the posterior arch of the atlas is a well-documented anomaly but a relatively rare condition. This condition is usually asymptomatic so most are diagnosed incidentally. There have been a few documented cases of congenital defects of the posterior arch of the atlas combined with atlantoaxial subluxation. We report a very rare case of congenital anomaly of the atlas combined with atlantoaxial subluxation, that can be misdiagnosed as posterior arch fracture.


Congenital anomaly of the atlas; Posterior arch fracture; Atlantoaxial subluxation

MeSH Terms

Cervical Atlas/*abnormalities
Diagnosis, Differential
Spinal Diseases/*diagnosis


  • Fig. 1 Lateral radiograph of the cervical spine suggested a posterior arch fracture.

  • Fig. 2 Trans-oral anterior-posterior radiograph showing atlantoaxial subluxation (arrow).

  • Fig. 3 Axial computed tomography at the level of C1 showing absent posterior arch of the atlas and atlantoaxial subluxation.

  • Fig. 4 Three-dimensional computed tomography reconstruction showing a defect of the atlas.

  • Fig. 5 T2-weighted magnetic resonance images showing no definite evidence of rupture of alar or transverse ligament and soft tissue swelling.

  • Fig. 6 Whole body bone scans showing normal findings.

  • Fig. 7 Flexion and extension radiographs showing absence of the posterior arch of the atlas without evidence of atlatoaxial instability (arrow).

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