PMC6942727_01
Case 1: cervical CT. (a) Complete C1 assimilation, C2-C3 congenital fusion block. (b) Previous C5-C7 ACDF. The C1 anterior ring is fracture displaced and positioned anterior to the clivus. The C1 posterior arch is fused to the occiput. (c) Left atlantoaxial subluxation. (d) Right condyle C1 lateral mass fracture dislocation.
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fig1
There was also distraction on the left side between the atlantoaxial joint (Figure 1).
Case 1: postoperative X-ray. Occipito-C6 PSIF.
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Open reduction of his craniocervical dissociation and occiput to C6 posterior segmental arthrodesis with placement of cortical screws in the occiput, laminar screws bilaterally at C2, and lateral mass screws bilaterally at C4, C5, and C6 (Figure 2) were performed.
Case 1: postoperative CT. (a) The reduction of the cortical step-off between the anterior arch of C1 and the clivus with partial reduction of the odontoid. (b) Right and (c) left. C1 screws were not placed. The vertebral arteries course bilaterally below the C1 ring. Lateral mass screw placed bilaterally at C4, C5, and C6. (d) Fixation to C2-C3 vertebrae block was obtained by placing laminar screws bilaterally at C2.
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Given the fact that the patient had a congenital fusion down to C3 as well as degenerative changes at C3-C4 and C4-C5, and previous ACDF at C5-C6 and C6-C7, his posterior cervical fixation was performed down into his subaxial cervical fusion in order to avoid short-term adjacent segment degeneration at C3-4 and C4-5 (Figure 3).
PMC6942727_02
Case 2: cervical CT. C1 congenital partial assimilation to the skull base. (a) The right C1 lateral mass is partially fused with the right occipital condyle. The left C1 lateral mass is completely fused to the left condyle. The tip of the dens is dysplastic and asymmetrically positioned towards the left lateral mass. (b) The rachischisis of the C1 posterior arch. (d, e) Acute fracture dislocation of the previously right and left lateral mass assimilation, respectively.
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C1 lateral mass (Figure 4). Cervical computed tomography angiography (CTA) did not reveal any vascular injury.
Case 2: intraoperative image. (A) Occiput. (B) C2 vertebra. (Upper arrow) left VA coursing above the free C1 posterior ring. (Thick arrow) right VA fused C1 posterior ring assimilated to the occiput.
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fig5
Intraoperatively, significant instability between the occipital to C2 region was noticed as well as an abnormal vertebral artery (Figure 5).
Case 2: postoperative X-ray. Occipito-C6 PSIF.
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On the left side, the vertebral artery traversed underneath the fused occiput-C1 ring, whereas, on the right side, the C1 posterior arch was free of the occiput and the vertebral artery traversed above this (Figures 6 and 7).
Case 2: CT postoperative. Anatomic alignment with reduction of the atlantooccipital fracture dislocation with bilateral C1, C2, and C3 lateral mass screws.
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On the left side, the vertebral artery traversed underneath the fused occiput-C1 ring, whereas, on the right side, the C1 posterior arch was free of the occiput and the vertebral artery traversed above this (Figures 6 and 7).