Intervertebral fusion sites in patients with ankylosing spondylitis: A computed tomography study

Objectives To examine intervertebral fusion sites along the whole spine of patients with ankylosing spondylitis using computed tomography. Methods This retrospective study examined intervertebral fusion of five sites (anterior/posterior vertebrae, left/right zygapophyseal joints, and spinous process) on 23 vertebrae in the cervical, thoracic, and lumbar regions of the spine in 40 patients diagnosed with ankylosing spondylitis at our institute between January 2004 and December 2022. Results Mean age [& PLUSMN; standard deviation (SD)] was 40.5 (& PLUSMN; 17) years, and mean disease duration (& PLUSMN; SD) was 11.4 (& PLUSMN; 10.5) years at computed tomography evaluation; 55.9% were human leukocyte antigen B-27-positive. Fifteen (37.5%) patients showed intervertebral fusion in the thoracic and/or cervical regions, but not in the lumbar region. Fusion of posterior vertebrae was observed most frequently in the thoracic region, compared to the cervical and lumbar regions. In particular, more than half of the patients showed fusion of posterior vertebrae Th4-Th5 to Th7-Th8. Conclusions In 37.5% of patients, intervertebral fusion was evident in the thoracic and/or cervical regions but not in the lumbar region. The most common site and region of intervertebral fusion were the posterior vertebrae of the middle thoracic region.