Correlation and differences in cervical sagittal alignment parameters between cervical radiographs and magnetic resonance images.

PURPOSE: Although cervical alignment is better assessed using standing radiography than supine magnetic resonance imaging (MRI), few studies have investigated this. This study aimed to investigate the difference in alignment between standing radiographs and supine MRI images, and assess whether neck position affects the cervical parameters and neurological changes.

METHODS: We analyzed 53 patients, measuring the O-C2 angle, C2-7 angle (the distinction between the lordotic and kyphotic groups), T1 slope, neck tilt, thoracic inlet angle, and the C2-7 sagittal vertical axis. Inter- and intra-group analyses were conducted to identify any difference between standing radiography and supine MRI. Statistical differences between the cervical parameters were compared.

RESULTS: Strong correlations were noted between the equivalent parameters in the radiographs and MRI images, whereas no significant difference was observed in C2-7 angle in the kyphotic group between the radiographs and MRI images, or for neck tilt between the radiographs and MRI images. However, in the lordotic group, the C2-7 angle was significantly different between the two types of images and larger in the radiographs than in the MRI images (C2-7 angle in the radiographs: C2-7 angle in the MRI images: 4.49°, p < 0.001).

CONCLUSIONS: Neck tilt was a constant parameter. The C2-7 angle in the kyphotic group was similar between the standing radiographs and the supine MRI images; however, the C2-7 angle in the lordotic group was different. Therefore, we recommend that standing cervical radiographs should be preoperatively obtained for all surgical patients. The slides can be retrieved under Electronic Supplementary Material.