Study on CT classification and evaluation methods for the degree of thoracoabdominal folded deformity in ankylosing spondylitis

English Keywords:Ankylosing spondylitis  Thoracolumbar kyphosis  Thoracoabdominal folded deformity  Thoracoabdominal folded angle  Distances between xiphoid process and superior edge of the pubis

English Abstract:

  【Abstract】 Objectives: To explore the CT classification and evaluation methods of thoracoabdominal folded deformity in ankylosing spondylitis(AS). Methods: A retrospective analysis was conducted on 31 patients with AS thoracolumbar kyphosis who underwent thoracolumbar CT examinations between July 2017 and January 2024. There were 28 males and 3 females, with an average age of 45.0±8.9 years. The thoracoabdominal folded angle(TAFA) and the distances between xiphoid process and the superior edge of the pubic symphysis(XP) were measured on the mid-sagittal plane of thoracolumbar CT. The global kyphosis(GK), thoracic kyphosis(TK), and lumbar lordosis(LL) Cobb angle and sagittal vertical axis(SVA) were measured on the full-length lateral radiograph of the spine. According to the effect of sagittal lumbar physiological curvature on the change of abdominal volume, a CT classification of AS thoracoabdominal folded deformity was innovatively classified into three types, type I when there was physiological lordosis in the lumbar spine, type Ⅱ when the physiological curvature of the lumbar spine became straight, and type Ⅲ when there was lumbar kyphosis deformity. According to TAFA, type Ⅲ patients were divided into two subtypes: TAFA>90° was subtype A, and TAFA≤90° was subtype B. Five trained spinal surgeons independently evaluated and classified the clinical data of patients(with a 10d interval), and used Kendall′s W-test to analyze the consistency of multiple observation results. Using one-way analysis of variance to compare the differences in the above measurement parameters between different types. Results: Among the 31 patients, there were 5 cases of thoracoabdominal folded deformity type Ⅰ, 8 cases of type Ⅱ, 12 cases of type ⅢA, and 6 cases of type ⅢB. The Kendall′s W consistency coefficient for inter-observer classification was 0.954(P<0.001). The average GK, TK, LL, SVA, TAFA, and XP of patients were 83.7°±29.9°, 48.7°±21.3°, -13.9°±25.3°, 22.8±14.9cm, 128.1°±50.5°, and 16.8±8.9cm, respectively; The Kendall′s W consistency coefficients between the different groups′ measurement values of TAFA and XP were 0.946(P<0.001) and 0.979(P<0.001), respectively; There were significant differences in TAFA and XP pairwise comparisons between different subtypes(P<0.001). Conclusions: CT imaging classification can objectively evaluate the thoracoabdominal folded deformity in AS, and the distance between the xiphoid process and pubic symphysis and the TAFA are important indicators for evaluating the thoracoabdominal folded deformity in AS.