PMC5386157_01
A: Preoperative computed tomography (CT) scans with angiography revealing C1 assimilation of the atlas and hypoplasia of vertebral artery of left side (arrow). B: Preoperative sagittal magnetic resonance imaging (MRI) T2-weighted showing ventral myelocompression.
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F1
Preoperative plain radiography and computed tomography (CT) scans revealed C1 assimilation and BI of the dens (Fig. 1A) and significant myelocompression by the C2 odontoid process (Fig. 1B). 
A: Photograph showing lift of the Halo vest gantry, B: Pre-traction, C: post-traction computed tomography scans revealing marked reduction of the odontoid process, and D: the m-cage .
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F2
Therefore, traction was performed gently using a Halo vest (Fig. 2A).  After the traction, CT scans revealed marked reduction of the odontoid process on the caudal side (Fig. 2B, C). Goel et al. used a custom-made spacer to distract the facet joints, but we used a 6-mm diameter threaded titanium cylindrical cage (Fig. 2D; m-cage ; Ammtec Inc., Tokyo ) on each side.
Postoperative right view (A), left view (B), coronal views (C, D), sagittal view (E) of computed tomography (CT) scans and magnetic resonance imaging (MRI) T2-weighted (F) showing reduced odontoid process of the axis. CT scans showing position of the dens at pre-treatment (G), post-traction (H), and post-operative (I) time points. CT scans taken 3 years after the surgery shows C1-2 facet fusion and no recurrence of basilar impression (J, K).
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F3
We expected to fuse solidly by fixing from the occipital bone to C5 (Fig. 3A-I). The atlantoaxial joints were considered to be bone-fused on C1-2 facet, and no recurrence of BI was noticed on CT scans performed 3 years post-operatively (Fig. 3J, K).