Novel 2 Radiographical Measurements for Atlantoaxial Instability in Children With Down Syndrome

Study Design. A retrospective case-control study. Objective. To assess the usefulness and reproducibility of 2 novel safe and simple radiographical measurements for atlantoaxial instability in children with Down syndrome. Summary of Background Data. In pediatric atlantoaxial instability, early diagnosis is important for improved outcomes because of poor postoperative recovery in progressed neurological symptoms. Conventional dynamic radiography of the cervical spine is associated with a potential risk of worsening neurological symptoms. Methods. We retrospectively reviewed the medical records of 50 patients (24 boys and 26 girls) with atlantoaxial instability associated with Down syndrome. Of the 50 children, 11 had undergone and 4 had been scheduled for surgery (surgical group). In this investigation, in addition to the atlas-dens interval (ADI) and space available for spinal cord (SAC), we measured C1 inclination angle and C1/4 SAC ratio on lateral radiographs of the cervical spine in the neutral position. To assess the diagnostic abilities of these indices to determine indication for surgery, receiver operating characteristic analysis of each index was performed, and their diagnostic abilities were compared using the area under the receiver operating characteristic curve. Moreover, we assessed reproducibility of our 2 proposed indices. Results. The discriminatory abilities of C1/4 SAC ratio (area under the receiver operating characteristic curve, 1.00)and C1 inclination angle (0.91) were comparable with those of ADI (0.98) and SAC (0.95). For the interobserver and intraobserver reliability of the novel indices, the correlation coefficients were in the range from 0.88 to 0.99. Correlation was observed between the ADI and C1/4 SAC ratio (r = 0.507, P < 0.01) and between the ADI and C1 inclination angle (r = 0.407, P < 0.01). Conclusion. The diagnostic abilities of the 2 novel radiographical measurements were comparable with those of ADI and SAC. Moreover, these novel measurements can be obtained safely on lateral radiographs of the cervical spine in the neutral position.