Osteoporosis is a common complication of AS even in the early stages of disease. Yet, AS is also characterized by new bone growth that leads to syndesmophytes formation and subsequent vertebral ankyloses.

Accordingly, previously-published studies have demonstrated large discrepancies in the reported incidence of osteoporosis, based on measurement of bone mineral density (BMD), in patients with AS ranging from 18.7% to 62%. Measurement of trabecular bone score (TBS) is a novel tool used to evaluate bone microarchitecture. Aim of the work: to compare bone quality using TBS between AS patients and healthy controls and to evaluate factors associated with TBS in patients with AS. Patients and methods: A total of 40 male AS patients recruited from Outpatient Clinic of Rheumatology, Mansoura University Hospital. 40 age-matched healthy males as matched control. TBS was analyzed using DXA images over exactly the same region as the lumbar BMD assessment (L1-L4). Lumbar spine DXA images were reanalyzed using TBS iNight software version 2.1 (Med-I maps, Merignac, France). Patients were divided in 3 TBS groups according to guidelines for fracture risk: any TBS >1.31 was considered as normal; TBS values between 1.23 and 1.31 were consistent as partially degraded structure; and any TBS <1.23 was considered as degraded structure

Inclusion Criteria:

• A total of 40 consecutive male AS patients were invited to participate in this study. Patients were recruited from Outpatient Clinic of Rheumatology, Mansoura University Hospital, between January and September 2019. AS was diagnosed according to modified New York criteria. During the same period, 40 age-matched healthy males were invited to participate in the study as a control group.

Exclusion Criteria:

• patients or controls with thyroid or parathyroid disorders, presence of chronic renal or liver disease, and use of any medication that could potentially interfere with bone metabolism including bisphosphonates, teriparatide, anticonvulsants, anticoagulants, calcium and corticosteroids. None of the participants was using vitamin D supplements.

data available upon request