PMC6744766_01
Dynamic lateral cervical radiographs: (a) in extension, Cobb and atlas angles are 65  and 47 , respectively. (b) In flexion, Cobb and atlas angles are decreased to -5  and 44 , respectively. Since atlas is loose with respect to axis, changes in atlas angle are invaluable in os odontoideum.
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F1
The dynamic lateral cervical X-rays showed a free-floating OO that compromised the oropharyngeal airway [Figure 1b]. The cervical lordosis was 65 in extension with 27  of atlas angulation [Figure 1a]. With neck flexion, the cervical lordosis decreased to -5  and the atlas angulation to 15  [Figure 1b].
(a) T1-weighted sagittal magnetic resonance imaging (MRI) of cervical spine shows an os odontoideum (OO) with atlantoaxial dislocation and narrowing of the cervicomedullary junction. The OO and atlas ring are engulfed in a soft tissue extending from os to axis. The posterior airway space is quite narrow in the MRI taken in neuter position (white dash). (b) T2-weighted sagittal MRI shows myelopathy at the cervicomedullary junction.
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F2
The cervical magnetic resonance imaging (MRI) showed atlantoaxial dislocation attributed to anterior displacement of the OO resulting in marked AP diameter canal narrowing at the cervicomedullary junction [Figure 2a]. The T2-weighted MRI showed a high intramedullary cord signal at the index level, consistent with myelomalacia versus edema [Figure 2b].
Computed tomography scan of the cervical spine, (a) axial view shows atlantoaxial dislocation. (b) Reconstructed sagittal view shows displaced os odontoideum (OO) - atlas ring forward displacement in jigsaw pattern; note posterior airway space is very narrow with the neck in neuter position. (c) Reconstructed coronal view shows the OO.
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F3
The sagittal CT showed the characteristic jigsaw pattern [Figure 3a]. Further, the posterior airway space was about 4 mm [Figure 3b and c].
Postoperative lateral cervical X-ray shows C1-C2 screw rod fixation (a) a few days after surgery. (b) Five years after surgery.
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F4
The patient underwent a C1-C2 posterior fusion [Figure 4a]. Five years later, he still has experienced no recurrence of OSA [Figure 4b].