• Atlantoaxial dislocation
• Cervical sagittal alignment and balance
• Os odontoideum
• Posterior atlantoaxial fusion

• Humans
• Atlanto-Axial Joint/surgery
• Atlanto-Axial Joint/diagnostic imaging
• Spinal Fusion/methods
• Spinal Fusion/adverse effects
• Male
• Joint Dislocations/surgery
• Joint Dislocations/diagnostic imaging
• Joint Dislocations/etiology
• Female
• Retrospective Studies
• Adult
• Cervical Vertebrae/diagnostic imaging
• Cervical Vertebrae/surgery
• Middle Aged
• Odontoid Process/surgery
• Odontoid Process/diagnostic imaging
• Joint Instability/surgery
• Joint Instability/diagnostic imaging
• Radiography
• Young Adult
• Adolescent
• Treatment Outcome

• 2021MS14 Second Military Medical University

• 3D-3D registration technology
• In vivo
• Posterior atlantoaxial fusion
• Six degree-of-freedom
• Three-dimensional kinematics

• Humans
• Spinal Fusion/methods
• Male
• Cervical Vertebrae/surgery
• Cervical Vertebrae/diagnostic imaging
• Cervical Vertebrae/physiopathology
• Female
• Range of Motion, Articular
• Atlanto-Axial Joint/surgery
• Atlanto-Axial Joint/diagnostic imaging
• Atlanto-Axial Joint/physiopathology
• Atlanto-Axial Joint/abnormalities
• Imaging, Three-Dimensional/methods
• Adult
• Middle Aged
• Biomechanical Phenomena
• Cone-Beam Computed Tomography
• Weight-Bearing/physiology
• Congenital Abnormalities

• Humans
• Male
• Atlanto-Axial Joint/surgery
• Atlanto-Axial Joint/diagnostic imaging
• Retrospective Studies
• Joint Dislocations/surgery
• Joint Dislocations/diagnostic imaging
• Female
• Adult
• Middle Aged
• Reoperation/methods
• Spinal Fusion/methods
• Treatment Failure
• Aged
• Adolescent
• Young Adult
• Treatment Outcome
• Decompression, Surgical/methods
• Postoperative Complications/etiology
• Child

• Humans
• Female
• Middle Aged
• Male
• Retrospective Studies
• Cervical Vertebrae/diagnostic imaging
• Cervical Vertebrae/surgery
• Lordosis/surgery
• Joint Dislocations/diagnostic imaging
• Joint Dislocations/surgery
• Joint Dislocations/complications
• Joint Instability/diagnostic imaging
• Joint Instability/etiology
• Joint Instability/surgery
• Spinal Fusion/adverse effects

Cervical sagittal balance is an important evaluation index of cervical physiological function and surgical efficacy. Subaxial kyphosis after atlantoaxial fusion is negatively associated with worse clinical outcomes and higher incidence of lower cervical disk degeneration.

This study aimed to confirm the factors that influence subaxial lordosis loss after posterior atlantoaxial fusion.

We performed a retrospective review of all patients following posterior C1–C2 fusion for atlantoaxial dislocation between January 2015 and December 2017. All charts, records, and imaging studies were reviewed for each case, and preoperative, immediate postoperative, and final follow-up plain films were evaluated. Comparing final follow-up and preoperative C2–C7 angle, patients were divided into two groups for further comparison: subaxial lordosis loss group and subaxial lordosis increase group.

A total of 18 patients were included in the review, with an average radiographic follow-up of 8.4 ± 3.7 months (range 6–17 months). Subaxial lordosis loss was observed in 5 cases (27.8%) at the final follow-up, whereas 13 cases had an increase in subaxial lordosis. The cervical sagittal parameters of preoperative and final follow-up between two groups were compared, the preoperative C2–C7 angle of the subaxial lordosis loss group was bigger than the subaxial lordosis increase group (27.6° ± 10.5° vs 10.5° ± 10.5°, P < 0.05), but there was no statistical difference in other parameters. Univariate chi-square analysis showed that reduction in subaxial lordosis after posterior atlantoaxial fusion was associated with preoperative C2–C7 angle ≥ 20° (χ² = 4.923, P = 0.026). However, Logistic regression analysis showed that the preoperative C2–C7 angle ≥ 20° was not an independent risk factor (OR = 0.147, P = 0.225).

Our study demonstrates that subaxial lordosis loss may occur after posterior atlantoaxial fusion, and preoperative C2–C7 angle ≥ 20° was a risk factor of postoperative loss of subaxial lordosis.

The anatomical features of the atlantoaxial spine increase the difficulty of complete and safe removal of atlantoaxial intradural extramedullary (IDEM) tumors. Studies concerning surgical interventions via a posterior approach are limited.

To investigate the safety and efficacy of atlantoaxial IDEM tumor resection using a one-stage posterior approach.

We retrospectively analyzed clinical databases for one-stage atlantoaxial IDEM tumor resection via a posterior approach between January 2008 and January 2018. The analyzed data included tumor position, histopathological type, pre- and post-operative Japanese Orthopedic Association (JOA) scores and Nurick grades, postoperative complication and recurrence status.

A total of 13 patients who underwent C1-C2 Laminectomy and/or unilateral facetectomy via the posterior approach were enrolled in the study. In all cases reviewed, total tumor resection and concomitant C1-C2 fusion were achieved. The average follow-up was 35.3 ± 6.9 mo (range, 26-49 mo). A statistically significant difference was noted between the preoperative JOA score (11.2 ± 1.1) and the score at the last final follow-up (15.6 ± 1.0) (P < 0.05). A statistically significant difference was noted between the preoperative Nurick grade (2.3 ± 0.9) and that at the last follow-up (1.2 ± 0.4) (P < 0.05). However, no statistically significant difference was noted between the preoperative and last follow-up C1-2 Cobb angle and C2-7 Cobb angle (P > 0.05). No mortalities, severe complications or tumor recurrence were observed during the follow-up period.

Total resection of atlantoaxial IDEM tumors is feasible and effective via a posterior approach. Surgical reconstruction should be considered to avoid iatrogenic kyphosis and improve spinal stability and overall clinical outcomes.

• Atlantoaxial spine
• Cervical spine
• Extramedullary tumors
• Intardural tumer
• Posterior approach
• Surgical resection

• Atlanto-axial
• C1-C2
• instability
• radiological parameters
• sagittal parameters
• trauma

• Atlantoaxial fusion
• Atlantoaxial instability
• Atlantodental interval
• Rheumatoid arthritis
• T1 slope

• cervical alignment
• craniovertebral junction
• posterior fixation
• risk factor
• subaxial kyphosis

Atlantoaxial subluxation (AAS) is characterized by excessive movement at the junction between the atlas (C1) and axis (C2) as a result of either a bony or ligamentous abnormality. Surgical intervention is a therapeutic choice for AAS. In addition to C1 laminectomy (LAM), surgical fixation for subluxation or instability is performed by various techniques. While surgical treatment options for AAS have increased, the outcomes of different surgical techniques remain unclear.

The authors conducted a retrospective analysis of the outcomes of 30 consecutive spinal surgeries performed for AAS patients, C1 LAM in 11 cases and C1/2 fixation in 19 cases. We investigated the correlation between the clinical outcomes and the surgical methods. We also examined the factors related to poor outcomes (the recovery rate of the Japanese Orthopedic Association score for cervical myelopathy < 40%) following AAS surgeries.

From a surgical method perspective, the patients in the C1 LAM group were older than those in the C1/2 fixation group (74.6 years vs 68.0 years), and the average recovery rate from the preoperative status was as follows: the C1 LAM group, 39.4%; the C1/2 fixation group, 49.8%. The C-JOA score was significantly improved after surgery in the C1/2 fixation group (from 9.8 to 13.1 points). The fixation technique seemed to successfully reduce C1/2 displacement. Each group exhibited a slight increase in the C1/2 angle and a decrease in the C2–7 angles after the operation. A higher preoperative atlantodental interval (ADI) was associated with good outcomes after the C1/2 fixation. The postoperative ADI was significantly reduced from 8.6 mm to 3.8 mm in the good outcome group after fixation. Patients with higher C1/2 angle showed good outcomes after C1 LAM. Despite the good neurological improvement, the C1/2 fixation method showed higher complication rates compared with C1 LAM method.

The results of this study showed that the C1/2 fixation technique exhibited effectiveness in terms of neurological recovery. However, there was a high complication rate in surgeries for AAS, especially in the C1/2 fixation. C1 LAM would be considered for high-risk AAS cases such as elderly patients with multiple comorbidities.

• Atlantoaxial subluxation
• Atlantodental interval
• Fixation
• Laminectomy
• Spine surgery

Retrospective case analysis.

We hypothesized that larger the C1–C2 fusion angle, greater the severity of the sagittal malalignment of C0–C1 and C2–C7.

In our experience, instances of sagittal malalignment occur at C0–C1 and C2–C7 following atlantoaxial fusion in patients with Os odontoideum (OO).

We assessed 21 patients who achieved solid atlantoaxial fusion for reducible atlantoaxial instability secondary to OO. The mean patient age at the time of the operation was 42.8 years, and the mean follow-up duration was 4.9 years. Radiographic parameters were preoperatively measured and at the final follow-up. The patients were divided into two groups (A and B) depending on the C1–C2 fusion angle. In group A (n=11), the C1–C2 fusion angle was ≥22°, whereas in group B, it was <22°. The differences in the radiographic parameters of the two groups were evaluated.

At the final follow-up, the C1–C2 angle was increased. However, this increase was not statistically significant (18° vs. 22°, p=0.924). The C0–C1 angle (10° vs. 5°, p<0.05) and C2–C7 angle (22° vs. 13°, p<0.05) significantly decreased. The final C1–C2 angle was negatively correlated with the final C0–C1 and C2–C7 angles. The final C0–C1 angle (4° vs. 6°, p<0.05) and C2–C7 angle (8° vs. 20°, p<0.05) were smaller in group A than in group B. After atlantoaxial fusion, the C0–C1 range of motion (ROM; 17° vs. 9°, p<0.05) and the C2–C7 ROM (39° vs. 31°, p<0.05) were significantly decreased.

We found a negative association between the sagittal alignment of C0–C1 and C2–C7 after atlantoaxial fusion and the C1–C2 fusion angle along with decreased ROM. Therefore, overcorrection of C1–C2 kyphosis should be avoided to maintain good physiologic cervical sagittal alignment.

• Atlantoaxial fusion
• Atlantoaxial instability
• Os odontoideum
• Sagittal alignment

• Adult
• Atlanto-Axial Joint/injuries
• Atlanto-Axial Joint/surgery
• Cervical Vertebrae/surgery
• Decompression, Surgical
• Female
• Humans
• Joint Dislocations/surgery
• Kyphosis/surgery
• Male
• Middle Aged
• Patient Reported Outcome Measures
• Spinal Fusion
• Treatment Outcome

The Magerl and Goel-Harms techniques have been reported to produce excellent treatment outcomes in cases of atlantoaxial subluxation, but they also carry a risk of vertebral artery injuries. In order to completely prevent such injuries, we developed a surgical procedure, involving bone grafting between the C1 posterior arch and C2 lamina with clamp- or hook-and-rod-based fixation combined with the insertion of an interference screw into the posterior atlantoaxial joint.

This was a retrospective single-center study. The subjects were 58 patients in whom atlantoaxial subluxation was treated with the abovementioned procedure after 1995 (33 patients with rheumatoid arthritis (RA group) and 25 patients without rheumatoid arthritis (non-RA group)). The clinical outcomes and imaging findings of anterior subluxation at ≥ 2 years after surgery were compared between the RA and non-RA groups.

No vertebral artery injuries occurred during surgery. Seven and two patients died during the follow-up period in the RA and non-RA groups, respectively, but none of these deaths were associated with surgery. At ≥ 2 years after surgery, the visual analogue scale score, Japanese Orthopaedic Association score, and Ranawat classification had significantly improved in both groups (p < 0.001). Radiologically, bone fusion was noted in all patients. Significant changes in the atlas-dens interval (ADI) were seen immediately after surgery in both groups (p < 0.001). In the non-RA group, significant changes in the corrected atlantoaxial height were observed immediately after surgery (p < 0.01), and loss of correction was seen at the final follow-up, but it was not significant (p = 0.1965). No significant changes were noted in any other parameter. Regarding the postoperative alignment of the cervical spine, lordosis tended to decrease, but additional surgery was only performed in one patient, who had developmental stenosis at the mid-lower level and belonged to the RA group. No reoperations due to fused adjacent segmental disease or exacerbated curvature were required.

In the present study, no vertebral artery injuries occurred during surgery, and no major perioperative complications developed. Favorable clinical outcomes were observed at ≥ 2 postoperative years although the patients’ diseases varied. This procedure produced superior outcomes, especially in terms of spinal correction and the maintenance of the ADI.

• Atlantoaxial subluxation
• Hook-rod constructs
• Interference screw
• Vertebral artery injury

• Adjacent segment degeneration
• Atlantoaxial
• Occipitoaxial
• Risk factor

• Adult
• Atlanto-Axial Joint/diagnostic imaging
• Atlanto-Axial Joint/surgery
• Female
• Humans
• Intervertebral Disc/diagnostic imaging
• Intervertebral Disc/pathology
• Intervertebral Disc Displacement/etiology
• Joint Instability/etiology
• Joint Instability/surgery
• Male
• Middle Aged
• Postoperative Complications
• Radiography
• Retrospective Studies
• Risk Factors
• Spinal Fusion/adverse effects
• Spondylarthritis/complications
• Spondylarthritis/diagnostic imaging
• Spondylarthritis/surgery

• C1–C2 fusion angle
• Cervical sagittal alignment
• Hyperlordotic fusion
• Non-rheumatoid arthritis patients
• Overreduction
• Posterior C1–C2 fusion

• Instability
• Outcome
• Polyaxial screw
• Rheumatoid arthritis
• Subaxial spine
• Upper cervical spine

• Adult
• Aged
• Arthritis, Rheumatoid/complications
• Atlanto-Axial Joint/surgery
• Bone Screws/adverse effects
• Female
• Humans
• Joint Dislocations/etiology
• Joint Dislocations/surgery
• Male
• Middle Aged
• Postoperative Complications/diagnostic imaging
• Postoperative Complications/epidemiology
• Spinal Fusion/adverse effects
• Spinal Fusion/methods

• 1012 MO CR

• cervical spine
• distal junctional disease
• occipitothoracic fusion
• rheumatoid arthritis
• sagittal alignment

• direct posterior reduction
• fracture odontoid
• irreducibility
• traumatic atlantoaxial dislocation

We report a very rare case of atlantoaxial subluxation (AAS) with persistent first intersegmental artery (PFIA) and assimilation in the atlas (C1) vertebra. This case demonstrates the difficulty of deciding on a surgical strategy for complex anomalies. A 63-year-old man presented with gait disturbance, neck pain, and severe dysesthesia in his left arm. Past history included a whiplash injury. Dynamic X-ray studies demonstrated an irreducible AAS and assimilation of C1. This subluxation was slightly deteriorated in an extended position. A three-dimensional computed tomography angiography (3DCTA) indicated that the PFIA was located on the left side. We performed a C1 posterior arch resection and C1 lateral mass–axis pedicle screw (C1LM–C2PS) fixation using the modified technique of skewering the occipital condyle and C1 lateral mass. The patient had no postoperative morbidity and his symptoms disappeared immediately after operation. Complex anomalies cause difficulty in determining surgical strategy although several surgical methods for simple craniovertebral junction anomaly have been reported. To avoid significant morbidities associated with vertebral artery injury, surgical strategies for these complex conditions are discussed. The modified technique of a C1 lateral mass screw penetrating the occipital condyle is a viable treatment option.

• AANS/CNS
• American Association of Neurological Surgeons/Congress of Neurological Surgeons
• Arthrodesis
• Atlantoaxial
• C1-2
• C1-C2
• CI
• Confidence interval
• TAS
• Transarticular screw
• VAI
• Vertebral artery
• Vertebral artery injury