The severity of basilar invagination and atlantoaxial dislocation correlates with sagittal joint inclination, coronal joint inclination, and craniocervical tilt: a description of new indexes for the craniovertebral junction.

BACKGROUND: Joint-distraction and intra-operative manipulation surgeries to correct basilar invagination (BI) and atlantoaxial dislocation (AAD) are becoming standard procedures. However, current data are unable to aid in the understanding of normal and abnormal morphology of the C1/C2 joints. OBJECTIVE: To study various aspects of C1/C2 joint morphology to create normative and patient data on joint abnormalities that could provide the surgeon with objective data for surgical planning and approach. METHODS: Seventy patients (age, 15-45 years) were compared with an equal number of age- and sex-matched control subjects (age, 21.9±8.2 years) with irreducible BI and AAD from a developmental origin (May 2010-July 2013). Joint anatomy was studied with the use of thin-slice computed tomography scans. The joint parameters studied included sagittal joint inclination, craniocervical tilt, coronal joint inclination, surface area, joint overlap index, and joint reciprocity. The severity of BI and the severity of AAD were compared. RESULTS: Sagittal joint inclination and craniocervical tilt significantly correlated with both BI and AAD (P<.01). Coronal joint inclination correlated with BI (P=.2). The mean sagittal joint inclination value in control subjects was 87.15±5.65° and in patients with BI and AAD was 127.1±22.05°. The mean craniocervical tilt value in controls was 60.2±9.2° and in patients with BI and AAD was 84.0±15.1°. The mean coronal joint inclination value in control subjects was 110.3±4.23° and in patients with BI and AAD was 121.15±14.6°. CONCLUSION: This study has demonstrated for the first time the important role of joint orientation and its correlation with the severity of BI and AAD and has described new joint indexes.