Study design: Retrospective radiographic study.
Purpose: Predict the variability of the center of gravity of head (COG) relative to the global cervical sagittal alignment (SVA).
Background: Cervical lordosis, thoracic kyphosis, lumbar lordosis, and pelvic incidence are considered interrelated, with changes in SVA causing reciprocal changes to bring the head over pelvis. The implications of cervical deformities have generated more interest recently, and it has been shown that poor cervical alignment is associated with poor clinical outcomes.
Methods: Patients were selected from the imaging server of a single institution with adult spinal deformity (ASD) and SVA, who underwent surgical correction from 2008 to 2013. Three observers performed the measurements, and intraclass correlation coefficient (ICC) was measured for inter and intraobserver reliability. Group 1 was patients with unbalanced spines (C7-SVA > 5 cm) preoperatively and corrected to full balanced spine (C7-SVA < 5 cm) until last follow-up. Group 2 was improved in sagittal balance after surgery and maintained SVA correction until last follow-up, but not fully balanced.
Results: Fifty-five patients met the inclusion criteria, 42 patients improved in SVA after surgery, and 13 showed no improvement. Twenty-three patients kept full balanced measurements until last follow-up, and 19 patients maintained not-full balanced spine. In group 1, there was no change in pre and postoperative parameters except for C2-CL (21.74° vs 16.91°, P = .033). It was similar in group 2, no differences except for C2-CL (21.67° vs 17.81°, P = .018).
Conclusion: Parameters in this study failed to yield predictable relationships when compared to changes in SVA. The position of COG may be independent of global SVA.
Clinical relevance: This study aims to improve our understanding of the dynamic changes and relationships of the regional and global spinal parameters with regard to spinal deformity corrective surgeries in adults.
Level of evidence: III.
Keywords: adult spine deformity; center of gravity; cervical sagittal balance; cervical spinal parameters; sagittal vertical alignment.