Cervical Sagittal Alignment in Patients With Basilar Invagination.

STUDY DESIGN: Retrospective study. OBJECTIVE: To present a morphological map of cervical sagittal alignment in basilar invagination (BI), a congenital anomaly of the craniovertebral junction, and contribute to a comprehensive understanding of cervical sagittal alignment in congenital cervical deformities. SUMMARY OF BACKGROUND DATA: Ideal cervical sagittal alignment and surgical targets are debated by scholars. However, most of the literature focuses on the description of cervical sagittal alignment in acquired cervical diseases and normal subjects and few on congenital cervical spine deformities. MATERIALS AND METHODS: This study analyzed cervical spine lateral radiographs of 87 BI patients and 98 asymptomatic subjects. They were analyzed for cranial, cervical spine, and thoracic inlet parameters. RESULTS: Patients with BI manifested significantly larger values for the following parameters than asymptomatic subjects: cranial tilt, cranial incidence angle, sagittal vertical axis (SVA) CGH-C7, C2-C7 angle, cervical tilt, and significantly smaller values for the following parameters: cranial slope, C0-C2 angle, C0-C7 angle, SVA C2-C7, spine tilt, thoracic inlet angle, and neck tilt. In the BI group, SVA C2-C7 was the cervical parameter most strongly correlated with the cranial, cervical spine, and thoracic inlet parameters, and was smaller in BI patients with fusion (atlanto-occipital assimilation) than in those without. CONCLUSION: A significant difference was observed between BI patients and asymptomatic subjects. BI patients have craniums tilted forward and downward, smaller upper cervical lordosis, larger lower cervical lordosis, and smaller thoracic inlet angle. In BI patients, the SVA C2-C7 is an important parameter in cervical sagittal alignment. In both individuals with congenital anomalies of the craniovertebral junction and the asymptomatic population, cervical spine alignment is significantly associated with cranial alignment, particularly thoracic inlet alignment.

Anatomical analysis of the C2 pedicle in patients with basilar invagination.

PURPOSE: To evaluate and describe the morphologic features of the C2 pedicle in patients with basilar invagination (BI) for informing the placement of pedicle screws. C2 pedicle screw placement is an important surgical technique for the treatment of atlantoaxial instability in patients with BI. However, no systematic and comprehensive anatomical study of the C2 pedicle in patients with BI has been reported. METHODS: The data from 100 patients diagnosed with BI (BI group) and 100 patients without head or cervical disease (control group) were included in the study. Radiographic parameters, including the pedicle width, length, height, transverse angle, lamina angle, and superior angle, were measured and analyzed on CT images. After summary analysis, the effect of C2-3 congenital fusion on C2 pedicle deformity in patients with BI was also investigated. RESULTS: The width, length, and height of the C2 pedicle of the BI patients were smaller than those of the control group. The pedicle cancellous bone was smaller in the BI group, while no significant difference in cortical bone was observed. In total, 44% of the pedicles were smaller than 4.5 mm in the BI group. Patients with C2-3 congenital fusion presented with smaller pedicle transverse angles and larger pedicle superior angles than those without fusion. Wide variations in the left and right angles of the pedicle were observed in the BI group with atlantoaxial dislocation or atlantooccipital fusion. CONCLUSION: The C2 pedicle in the BI group was thinner than that in the control group due to a smaller cortical bone. Cases of C2-3 congenital fusion, atlantoaxial dislocation, and atlantooccipital fusion displayed variation in the angle of the C2 pedicle.