Sacroiliac joint fusion in patients with ankylosing spondylitis is associated with hip involvement

Objective: Ankylosing spondylitis (AS) is a progressive inflammatory disease that affects the axial skeleton, and often associated with hip involvement. However, the causative factors for radiological hip involvement in patients with AS are not well characterized. This study aimed to investigate the factors associated with hip involvement in patients with AS. Methods: Sixty-seven patients (134 hips) diagnosed with AS who qualified the modified New York criteria at our institution between January 2005 and June 2022 were enrolled. Patients were divided into two groups: the hip involvement group (BASRI-hip score >= 2 points) and the normal group (BASRI-hip score <2 points). Demographic, clinical and radiographic characteristics were compared between the two groups. Results: Twenty-six patients (38.8%) had radiological hip involvement, of which 23 (88.5%) patients were male. There were significant between-group differences with respect to sacroiliac joint fusion, crossover sign, high centre edge angle and low sharp angle (P < 0.05). On logistic regression analysis, older age, sacroiliac joint fusion and pincer type were identified as independent risk factors for hip involvement. Conclusion: AS with hip involvement was significantly more likely to involve sacroiliac joint fusion, which suggested that mechanical stress in adjacent joints and reduced spinopelvic range of motion may influence hip involvement. (c) 2023 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.