Compensatory modulation for severe global sagittal imbalance: significance of cervical compensation on quality of life in thoracolumbar kyphosis secondary to ankylosing spondylitis

To investigate the cervical compensation pattern and to clarify relationships between cervical compensation and quality of life (QOL) in ankylosing spondylitis (AS) patients with thoracolumbar kyphosis.

A cross-sectional study of consecutive AS patients with thoracolumbar kyphosis was performed. Forty-four patients with hyperlordotic cervical spine were assigned to group A and sixteen with kyphotic cervical spine in group B. Sagittal parameters were measured and compared, including T1 slope, cervical lordosis (CL), cervical sagittal vertical axis (C-SVA), global SVA and global kyphosis (GK). Independent factors for cervical compensation were identified. To exclude confounding variables while comparing QOL between patients with hyperlordotic and kyphotic cervical spine, 31 patients were selected as group A-1, similar to 13 patients in group B-1 in the distribution of matching variables such as age, gender, course of disease, GK, global SVA and radiographic progression assessment for AS. The QOL was assessed by Neck Disability Index (NDI) and other indices.

Mean C-SVA was significantly lower in group A than in group B, whereas mean T1 slope, global SVA and GK were significantly larger in group A. T1 slope (36.0 %) was the independent factor for CL. T1 slope was correlated with CL, GK and global SVA in group A. Group A-1 showed lower NDI score. CL (59.6 %) independently affects NDI.

Notable cervical compensation exists in AS patients with thoracolumbar kyphosis. The cervical compensation responsive to global imbalance was mediated by T1 slope. AS patients with hyperlordotic cervical spine present with better QOL than patients with kyphotic cervical spine.