How cervical and cervicothoracic scoliosis influence the atlantoaxial joint

Children with cervical or cervicothoracic congenital scoliosis are limited in their ability to compensate for the main curve of the deformity because there are only a few mobile segments in their cervical spine. Over the years, we have frequently observed coronal atlantoaxial dislocation (CAAD) in a lateral direction (from left to right or vice versa) in these patients. It was anticipated that CAAD might compensate for the horizontal position of the head, and it is hypothesized that CAAD depends on the degree of scoliotic deformity. Thus, the aim of our study was to investigate whether there is a correlation between CAAD and scoliosis parameters in these patients.

Retrospective analysis was performed based on CAT scans and preoperative X-rays of patients with cervical and cervicothoracic scoliosis with an apex between C4 and T6. Seventeen patients, with a mean age of 7.25 years, who were 9 girls and 8 boys, and who were treated between 2006 and 2022 were included. Cobb`s angle of the main curve (CA-MC), Cobb`s angle of the secondary curve (CA-SC), and T1-, C2- and UEV (upper end vertebra) tilt were measured on whole-spine radiographs in the standing position. The CAAD was measured via coronal CAT scan reconstruction and defined as the difference in the distances of the lateral masses to the midline of the axis. Pearson`s linear correlation coefficients (r) were determined using SPSS to evaluate correlations between CAAD and the measured parameters. p < 0.05 indicated statistical significance.

CAAD toward the convex region in patients with scoliosis was typically observed; the mean CAAD was 3 mm ± 3.7 mm. The mean CA-MC was 46° ± 13°, the mean CA-SC was 16° ± 9.6°, the mean T1 tilt was 17° ± 8.8°, the mean C2 tilt was 9°± 8.8°, and the mean UEV tilt was 24° ± 7.2°. There was a strong linear correlation between CAAD and CA-MC (r = 0.784, p < 0.001), C2 tilt (r = 0.745; p < 0.001), and UEV tilt (r = 0.519; p = 0.033). There was no correlation between CAAD and either CA-SC or T1 tilt.

Children with cervical or cervicothoracic scoliosis tend to have a CAAD toward the convexity of the scoliosis that correlates to CA-MC, C2-tilt, and UEV-tilt. CAAD may be seen as a compensatory mechanism to keep the head in a horizontal position. Severe or progressive CAAD may result in destruction of the atlantoaxial joint, including severe complaints, thus necessitating close follow-up and possibly early surgical treatment. Moreover, CAAD might be a useful additional radiographic parameter to be checked in future scoliosis studies.