The Usefulness of Trabecular Bone Score in Patients with Ankylosing Spondylitis

Abstract

Objectives: To reveal the usefulness of the trabecular bone score (TBS) for assessing bone strength in patients with ankylosing spondylitis (AS) by the comparison with dual energy x-ray absorptiometry (DXA) methods. Methods: Total of 215 AS patients were enrolled from a single university hospital in Korea. Demographic and clinical information was collected by questionnaires and medical record review. Patients completed X-ray of cervical and lumbar spine (L-spine), and quantification of spine ankyloses were determined by modified Stoke AS Spine Score (mSASSS). Hip, anteroposterior (AP) and lateral L-spine bone mineral density (BMD) was assessed by DXA methods. TBS was obtained from DXA using TBS iNsight software. Clinical characteristics and bone strength measurement results were compared between male and female patients. Prevalence of fracture history and bone strength measurement results were compared between high and low mSASSS group in male patients. Accuracy of each bone strength evaluation method to detect FRAX score of moderate or higher fracture risk was compared by ROC curves in patients aged ≥ 40. Correlations among each bone strength measurement method and mSASSS were examined. Results: The mean age was 49.9 ± 10.4, and mean disease duration was 118.5 ± 212.7 months. Male patients were 75.8 %. Male patients showed higher mSASSS than female patients [32.5 ± 23.1 vs. 13.5 ± 13.7, p<0.01]. In male patients, vertebral fracture history was marginally more prevalent in high mSASSS group [p=0.05] and only TBS was lower in this group [p<0.01]. TBS, hip BMD, and L-spine lateral BMD showed comparably high AUCs to detect FRAX-major osteoporotic fracture ≥ 10 % [AUCs ranged 0.72-0.76]. TBS negatively correlated with mSASSS in both male and female patients [p<0.01]. In contrast, L-spine AP BMD showed positive correlation with mSASSS in male patients. And, hip BMD and L-spine lateral BMD showed negative correlations with mSASSS only in female patients. Conclusions: TBS is a useful tool for assessing bone strength in patients with AS because it can predict the risk of vertebral fracture in AS patients, even in those with advanced spinal changes. Moreover, TBS is not influenced by spinal osteoproliferation in both male and female patients.