Sequential sagittal alignment changes in the cervical spine after occipitocervical fusion

Abstract

Background: There are few studies regarding sequential changes in the sagittal alignment of the upper and lower cervical regions of the spine after occipitocervical fusion (OCF). In addition, no comparisons of cervical sagittal alignment (CSA) between patients with craniocervical junction disorders (CJDs) and normal populations have been reported.

Aim: To compare the CSA of patients with CJDs with that of normal controls and investigate the sequential changes in the CSA of the upper and lower cervical spine after OCF.

Methods: Eighty-four patients who underwent OCF (OCF group) and 42 asymptomatic volunteers (control group) were included. Radiographic parameters, including the occipital to C2 angle (O-C2a), occipital and external acoustic meatus to axis angle (O-EAa), C2-7 angle (C2-7a), and pharyngeal inlet angle (PIA), were measured and compared pre- and postoperatively. The correlations among the parameters were analyzed using Pearson's correlation test.

Results: The O-C2a and PIA of the OCF group were smaller than those of the control group, while their O-EAa and C2-7a values were larger than those of the normal controls. There were no significant differences in O-C2a, C2-7a, or PIA in the OCF group at baseline, 1 mo, or the final follow-up after surgery. The Pearson's correlation results showed that there were significant correlations between the O-C2a and C2Ta, C2-7a, C2-7 sagittal vertical axis (SVA), and PIA at 1 mo after OCF surgery and between O-C2a and O-EAa, C2Ta, C2-7a, C2-7 SVA, and PIA at the final follow-up.

Conclusion: Patients with CJDs have a more kyphotic upper CSA and a more lordotic lower CSA than normal controls. The effectiveness of OCF surgery in restoring CSA may be limited by the realignment of the craniocervical junction being neglected. The reduction in O-C2a after OCF surgery may increase C2-7a and decrease PIA.

Keywords: Cervical spine; Craniocervical disorders; Dysphagia; Occipitocervical fusion; Sagittal alignment.

Figure 1

Representation of the radiographic measurements. O-C2a: The angle between the inferior endplate of C2 and the McGregor line; O-EAa: The angle formed by the McGregor line and the EA-line; C2Ta: The angle formed by the inferior endplate of C2 and the EA-line; C2-7a: The Cobb angle between the lower endplate of C2 and C7; T1 slope: The angle between the horizontal and the T1 superior endplate; C2-7 SVA: The horizontal distance between the C2 plumb line and the posterior corner of C7; PIA: The angle between McGregor line and the line that links the center of the C1 anterior arch and the apex of cervical sagittal curvature. O-C2a: O-C2 angle; O-EAa: Occipital and external acoustic meatus to axis angle; C2Ta: C2 tilting angle; C2-7a: C2-7 angle; SVA: Sagittal vertical axis; PIA: Pharyngeal inlet angle.

Figure 2

A 43-year-old woman developed dysphagia after occipitocervical fusion surgery. A: The preoperative O-C2 angle (O-C2a), C2-7 angle (C2-7a) and pharyngeal inlet angle (PIA) were 11.1°, 10.8°, and 93.8°, respectively; B: The OC2a and PIA decreased to -9.3° and 81.5°, respectively, while the C2-7a increased to 42.9° 1 mo postoperatively; C: At the 1-year follow-up, the O-C2a, C2-7a, and PIA were -8.9°, 38.2°, and 83.7°, respectively. O-C2a: O-C2 angle; C2-7a: C2-7 angle; PIA: Pharyngeal inlet angle.