Congenital Anomaly of the Atlas Misdiagnosed as Posterior Arch Fracture of the Atlas and Atlantoaxial Subluxation
A 28-year-old woman was referred to the emergency department with left hip pain, wrist pain and neck pain after being involved in a traffic accident. On physical examination, her neurologic system showed no abnormal findings. Roentgenographic studies showed left acetabular fracture and left distal radius fracture. A lateral cervical radiograph taken initially in the investigations suggested posterior arch fracture (). A trans-oral anterior-posterior view of the atlas revealed an atlantoaxial subluxation (AAS) (). Computed tomography (CT) images with three-dimensional (3D) reconstruction demonstrated the absence of the posterior arch and the presence of a persistent posterior tubercle. Like the cervical radiograph, there were signs of AAS in the CT images ( and ). Magnetic resonance images (MRI) showed no definite evidence of rupture of the alar or transverse ligament or soft tissue swelling ().\nNo evidence of traumatic injury was shown on whole body bone scinitigraphy (). The patient's neck pain resolved spontaneously. Post-recovery flexion and extension films revealed the absence of the posterior arch of the atlas but there was no evidence of atlantoaxial instability (). The patient was asymptomatic at a follow-up visit six months after the accident.