Relationship between characteristics of spinopelvic alignment and quality of life in Japanese patients with ankylosing spondylitis: a cross-sectional study

Background Studies on characteristic spinal deformities in Japanese patients with ankylosing spondylitis (AS) and data demonstrating a relationship between health-related quality of life (HRQOL) and spinopelvic alignment in these patients are lacking. Methods In this cross-sectional study, 50 patients with AS and without a surgical history, vertebral body fracture, or scoliosis as well as 30 control patients with degenerative lumbar kyphoscoliosis (DLKS) were included. Data collected included patient sex, age, spinopelvic parameters on sagittal full-spine standing radiographs, and HRQOL questionnaire responses. Student's t-test was used to compare the characteristics of spinopelvic parameters between the groups. A multiple regression analysis was performed to analyze correlations between spinopelvic parameters and HRQOL in the AS group. Results Global kyphosis (GK; T1-12 angle) was significantly greater in the AS group than in the DLKS group (P < 0.001), whereas the pelvic tilt (PT; posterior PT angle) was smaller in the AS group (P = 0.006). Radiographic parameters correlated with HRQOL in the AS group. Multiple regression analysis identified the sagittal vertical axis (SVA) and sacral slope (SS) as factors influencing the SRS-22 total score and SVA and GK as factors influencing Japanese Orthopaedic Association Back Pain Evaluation Questionnaire mental health (subdomain). Conclusions Patients with AS did not use lumbar lordosis or posterior PT to compensate for their large thoracic kyphosis due to spinopelvic ankylosis. These patients showed a unique compensation pattern. The correlation/regression analysis revealed a correlation between radiographic parameters and HRQOL in patients with AS, with particular importance of SVA, SS, and GK for clinical results in AS.