Background Osteoporosis is a well-recognized feature of axial spondyloartyhritis (ax-SpA) and an increased risk of vertebral fractures (VFs) has been reported in patients with SpA. The prevalence of VFs is highly variable across studies, up to 30%. These data are unexpected in a disease affecting a young population, predominantly males. These results could be related to differences in methods of diagnoses of VFs and in populations with highly variable duration of the disease. We hypothesized that the prevalence and incidence of VFs be lower than the ones previously reported, especially in early spondyloarthritis.

Objectives Our primary aim was to assess the prevalence of VFs in a cohort of early inflammatory back pain suggestive of early axial SpA and their incidence over 5 years.

Methods Study population: patients from the DESIR (DEvenir des Spondylarthropathies Indifférenciées Récentes) cohort, which is a french national longitudinal prospective cohort including adults between 18 and 50 years old, and presenting with inflammatory back pain suggestive of axSpA for less than 3 years. Follow-up is still ongoing, but the data presented here includes the first 5 years of follow-up. All patients had thoracic and lumbar spine X-rays at baseline, 2 years and 5 years. For this particular study, all radiographs of the DESIR cohort were centrally read by one reader, an expert in the field of the diagnosis of VFs according to Genant's method. Careful assessment was used to distinguish true VFs not to be mistaken with deformities. Using a temporal sequence of reading (i.e. unblinded for chronological order), an incident VF was defined as a change in the score of a vertebra from grade 0 to a subsequent grade 1 or more. All vertebrae between T4 and L4 were evaluated. In doubtful cases, an adjudication by two other senior experts was performed. Prevalence at inclusion and the incidence of VFs over the first 5 years of follow-up were described.

Results A total of 708 patients with inflammatory back pain were included in the DESIR cohort. Plain dorsolumbar spine X-rays were available for 694 patients, and thoracic and/or lumbar X-rays were available for 643 patients at baseline. Twenty eight VFs were identified in 21 patients (19 grade 1 VFs and 9 Grade 2 or 3 VFs); therefore, the prevalence of VFs was 4.5%.

Complete X-ray follow up between baseline and M60 was available for 433 patients. Seven incident VFs were identified in 6 patients: at 2 years 3 grade 1 VFs and 1 grade 2 VF were identified; and at 5 years, 2 grade 1 VF and 1 grade 2 or more VF were identified. The 5-year incidence of VFs was 1.6%.

Conclusions In this study focused on a population of early spondyloarthritis, the reported low prevalence of VFs of 4.5% and incidence of 1.6% confirm our hypothesis that the real prevalence and incidence of VF in SpA is probably much lower than what was reported in previous studies. These discrepancies might be explained by the variability in the methods of vertebral fracture's assessment as vertebral deformations might be inappropriately considered as fracture.

Disclosure of Interest None declared