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Background: Atlantoaxial fusion has been widely used for the treatment of atlantoaxial instability (AAI). However, atlantoaxial fusion sacrifices the motion of atlantoaxial articulation, and postoperative loss of cervical lordosis and aggravation of cervical kyphosis are observed. We investigated various factors under the hypothesis that the atlantodental interval (ADI) and T1 slope may be associated with sagittal alignment after atlantoaxial fusion in patients with rheumatoid arthritis (RA)., Methods: We retrospectively investigated 64 patients with RA who underwent atlantoaxial fusion due to AAI. Radiological factors, including the ADI, T1 slope, Oc-C2 angle, cervical sagittal vertical axis, and C2-C7 angle, were measured before and after surgery., Results: The various factors associated with atlantoaxial fusion before and after surgery were compared according to the upper and lower preoperative ADIs. There was a significant difference in the T1 slope 1 year after surgery (p = 0.044) among the patients with lower preoperative ADI values. The multivariate logistic regression analysis showed that the preoperative ADI (> 7.92 mm) defined in the receiver-operating characteristic curve analysis was an independent predictive factor for the increase in the T1 slope 1 year after atlantoaxial fusion (odds ratio, 4.59; 95% confidence interval, 1.34-15.73; p = 0.015)., Conclusion: We found an association between the preoperative ADI and difference in the T1 slope after atlantoaxial fusion in the patients with RA. A preoperative ADI (> 7.92 mm) was an independent predictor for the increase in the T1 slope after atlantoaxial fusion. Therefore, performing surgical treatment when the ADI is low would lead to better cervical sagittal alignment.

Study Design: Retrospective data analysis., Objective: To identify factors affecting the atlantodental interval, the Ranawat value, and subaxial translation after rheumatoid arthritis (RA) diagnosis. In addition, factors predictive for cervical spine instability (CSI) development after RA diagnosis were examined., Summary of Background Data: Development of CSI affects the prognosis and mortality of RA patients. Previous studies described that obesity is associated with reduced radiographic joint damage in RA patients. We hypothesized that body mass index (BMI) is also associated with radiographic cervical damage in RA patients., Methods: Cervical radiographs were taken at full flexion, neutral position, and full extension to measure the geometric length of the anterior atlantodental interval, the Ranawat value, and subaxial translation. These values were entered into multivariable linear regression analysis based on potential associated factors. Hazard ratios were calculated to identify independent factors predictive of CSI., Results: Of the patients diagnosed with RA between January 2005 and August 2015, 1611 who underwent at least one cervical radiograph were included. After adjusting for sex, age, BMI category, CSI, rheumatoid factor, and RA medication, multivariate analysis revealed that the risk of atlantoaxial subluxation in the underweight and normal BMI groups was about 1.6-fold (hazard ratio, 1.63; 95% CI, 1.10-2.43; P = 0.015) and 1.7-fold higher, respectively, than that in the obese group, and that the risk of vertical subluxation was about 2.5-fold (hazard ratio, 2.52; 95% CI, 1.32-4.83; P = 0.005) higher in the underweight group than in the obese group. We also found that the rheumatoid factor positivity was a predictive risk factor for CSI development., Conclusion: We identified risk factors predictive for CSI occurrence after RA diagnosis through cervical radiograph assessment. We found that BMI was an independent predictor for development of CSI. Further large-scale prospective studies are required to confirm these findings., Level of Evidence: 3.

Background: Rheumatoid arthritis (RA) is an autoimmune disease that often occurs in the atlantoaxial segment of the cervical spine and results in instability that can cause severe pain and neurologic symptoms. Thickening of soft tissue posterior to the odontoid process of the atlantoaxial segment is referred to as retro-odontoid soft tissue (ROST) thickness or pseudotumor. The mechanism of ROST thickness is still unknown., Methods: Among patients diagnosed with RA, those with cervical radiographs and magnetic resonance imaging records were selected for investigation of their clinical symptoms, laboratory findings, radiologic evaluation, and RA medication history., Results: A total of 199 patients were selected and divided into lower and upper median groups according to the ROST thickness value. In patients with RA, the median ROST thickness value was 2.3 mm (interquartile range, 1.4-3.4). The median value of the anterior atlanto-dens interval (ADI) was 2.4 mm, with a significant difference being observed between the lower and upper median ROST thickness groups (P = 0.001). Multivariable linear regression analysis revealed a correlation between Steinbrocker stage and the positivity of rheumatoid factor. For each unit increase in the Steinbrocker stage, the ROST thickness increased by 0.35 mm (β, -0.349; 95% confidence interval -0.643 to -0.055; P = 0.020). For every 1-mm increase in the ADI, ROST thickness decreased by 0.16 mm (β, -0.163; 95% confidence interval -0.264 to -0.062; P = 0.002)., Conclusions: This study showed a statistical correlation between ROST thickness and ADI related to biomechanical changes in the dynamic atlantoaxial segment, thereby suggesting the value of a prospective study., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Osteopenia and osteoporosis were independent predictive factors for higher atlantoaxial subluxation occurrence in patients with lower body mass index. Our findings suggest that patients with rheumatoid arthritis with osteopenia or osteoporosis, particularly those with lower body mass index (BMI), should be screened regularly to determine the status of their cervical spines., Introduction: Cervical spine involvement in rheumatoid arthritis (RA) patients may cause serious adverse effects on quality of life and overall health. This study aimed to evaluate the association between atlantodental interval (ADI), atlantoaxial subluxation (AAS), and systemic bone mineral density (BMD) based on BMI variations among established patients with RA., Methods: The ADI was transformed to the natural log scale to normalize distributions for all analyses. Multivariable linear regression analyses were used to identify independent predictive factors for ADI based on each BMD classification. Multivariate Cox regression analyses were also performed to identify independent predictive factors for the risk of AAS, which were classified by tertile groups of BMI., Results: A total of 1220 patients with RA who had undergone at least one or more cervical radiography and BMD assessments were identified and enrolled. We found that the association between BMD and ADI (β, -0.029; 95% CI, -0.059 to 0.002; p = 0.070) fell short of achieving statistical significance. However, the ADI showed a 3.6% decrease per 1 BMI increase in the osteoporosis group (β, -0.036; 95% CI, -0.061 to -0.011; p = 0.004). The osteopenia and osteoporosis groups showed about a 1.5-fold and a 1.8-fold increased risk of AAS occurrence among the first tertile of the BMI group., Conclusions: Our study showed a possible association between lower BMD and AAS occurrence in patients with RA with lower BMI. Further studies are needed to confirm our findings.

Background: Many surgical procedures have been introduced to manage atlantoaxial instability caused by rheumatoid arthritis (RA) to prevent complications and improve fusion rate. We report the surgical outcome between transarticular screw fixation (TAF) and C1 lateral mass-C2 pedicle screw fixation (C1LM-C2P) in patients with atlantoaxial instability from RA., Methods: Between 2002 and 2012, 58 patients were enrolled in the study. According to surgical procedures, patients were divided into 2 groups: group I who received TAF (n = 33) and group II who received C1LM-C2P (n = 25). Bony fusion was assessed by radiologic comparison immediately after the operation and 1 year postoperatively. In addition, complications and clinical and functional outcomes were evaluated., Results: Overall, bone fusion was achieved in 32 patients in group I (97%). In group II, the fusion rate was evaluated in 100% of patients. Complications (regardless of neurologic deterioration) were cable loosening and screw malposition in group I and violation into the vertebral canal and spinal canal in group II. There was no statistical significance in fusion rate, clinical outcomes, or complications. The 12-month atlantodental interval after operation for the C1LM-C2P group was significantly lower than that for the TAF group after adjusting for all variables., Conclusions: Two surgical techniques showed a good fusion rate by rigid fixation in the immediate postoperative period and fewer surgery-related complications in patients with RA. Because surgical complications are more likely during the learning curve (as with other surgical techniques), surgeons should carefully evaluate patients before surgery by radiologic and neurologic examinations., (Copyright © 2016 Elsevier Inc. All rights reserved.)