Non-traumatic posterior atlanto-occipital joint dislocation.

This report presents a case of non-traumatic posterior atlanto-occipital dislocation. A 36-year-old female was referred with a history of numbness of the extremities, vertigo and neck pain for 1 year. The patient had no history of trauma. The axial rotation of range of motion of the cervical spine was severely restricted. A lateral cervical radiograph in the neutral position demonstrated a posterior atlanto-occipital dislocation. A coronal view on a computed tomography (CT) reconstruction image showed a loss of angle of the bilateral atlanto-occipital joint, and a sagittal reconstruction view of CT images also demonstrated flatness of atlanto-occipital joint. Instrumented occipito-cervical fusion was performed after reduction. A lateral cervical radiograph in the neutral position 1 year after surgery showed the reduction of atlanto-occipital joint, moreover, it was maintained even in an extended position. The patient had neurologic improvement after surgery. Flatness of the bilateral atlanto-occipital joint may have induced this instability. Occipital-cervical fusion was chosen in the present case since the patient showed restricted axial rotation of the neck before surgery. The surgery improved the preoperative symptoms including the function of cervical spine evaluated by JOACMEQ.