Low Bone Turnover, Mineralization Impairment, and Cortical Alterations in Patients with Axial Spondyloarthritis: A Histomorphometric Study.

Patients with radiographic axial spondyloarthritis (r-axSpA) experience a higher prevalence of fragility fractures, though the pathophysiology of osteoporosis associated with this disease remains poorly understood. The objective of this study was to evaluate the histomorphometric data in r-axSpA patients. Male r-axSpA patients up to 55 years old were enrolled in this cross-sectional study. Clinical, lab, and imaging data, including spine X-Ray to evaluate vertebral fractures and new bone formation, as well as dual-energy X-ray absorptiometry (DXA) at spine, hip, and forearm and trabecular bone score (TBS), were performed in all patients. Transiliac histomorphometry was also underwent in all patients, and data were compared with 21 male cadavers' material. A total of 21 patients were included, with a mean age of 45.8 years, long disease duration (median 17.5 years), mostly white (66.7%) and positive for HLA-B27 (90.5%). The prevalence of DXA abnormalities and low TBS (≤ 1.338) was 42.8% and 57.1%, respectively. There was higher osteoid trabecular thickness (p = 0.027) and cortical bone changes, including reduced thickness (p = 0.031) and increased porosity (p = 0.015) in r-axSpA patients. In addition, a pattern of cortical trabecularization was observed in 52.3%. Dynamic evaluation revealed a longer mineralization lag time (p = 0.0074) and lower mineralized surface (p = 0.0029) and bone formation rate (p = 0.0074) in patients compared to reference values. Our results showed a pattern of low trabecular remodeling, bone mineralization impairment, as well as cortical thickness and porosity abnormalities in men with r-axSpA. These findings may impact future treatment of bone fragility in this disease.