Low pelvic incidence is associated with Andersson lesions in ankylosing spondylitis patients with kyphosis

Introduction/objectives This study was to investigate the role of pelvic incidence (PI) in the development of Andersson lesions (ALs) in ankylosing spondylitis (AS) patients with kyphosis and to evaluate the difference in sagittal spinopelvic parameters between inflammatory ALs and mechanical ALs. Method A total of 135 AS patients with kyphosis were reviewed. The patients were classified into AL group and non-AL group based on the presence or absence of ALs. Additionally, AS patients with ALs were also classified as either inflammatory or mechanical lesions depending on the radiological features of the lesions. The sagittal spinopelvic parameters of all these AS patients were measured and compared. Logistic regression analysis was performed to determine the powerful variables for predicting ALs in AS patients. Results ALs were detected in 34 patients (25.2%) of the total 135 AS patients. The mean PI of the AL group was 40.0 degrees, which was significantly lower than that (48.3 degrees) of the non-AL group (P < 0.001). No statistically significant difference was observed in PI (P = 0.350) between the inflammatory lesion group and the mechanical lesion group. Logistic regression analysis showed that only PI was a statistically significant risk factor for ALs (P < 0.001) and was negatively correlated with ALs (odds ratio = 0.76). Conclusions These data suggest that low PI is closely associated with ALs in AS patients with kyphosis and that it might be a possible risk factor for the development of ALs. Moreover, both inflammatory and mechanical ALs patients had similarly low PI.