Relationship between spinal structural damage on radiography and bone fragility on CT in ankylosing spondylitis patients

Marine Fauny,Damien Loeuille,Eliane Albuisson,Astrid Pinzano,Caroline Morizot,Frank Verhoeven,Edem Allado,Isabelle Chary-Valckenaere

doi:10.1038/s41598-021-88838-9

Abstract

To evaluate whether the risk of bone fragility on computed tomography (CT) (scanographic bone attenuation coefficient of the first lumbar vertebra (SBAC-L1)) is associated with the severity of spine structural involvement (mSASSS) in patients with ankylosing spondylitis (AS). This retrospective study included AS patients, followed from 2009 to 2017, who fulfilled the New York criteria and who underwent thoraco-abdomino-pelvic CT and radiography (spine, pelvis). The structural involvement was retained for mSASSS ≥ 2. The SBAC-L1 was measured in Hounsfield units (HU). A SBAC-L1 ≤ 145 HU was used to define patients at risk of vertebral fracture (VF). A total of 73 AS patients were included (mean age: 60.3 (± 10.7) years, 8 women (11%), mean disease duration: 24.6 years (± 13.9)). Sixty patients (82.2%) had a mSASSS ≥ 2 (mean score 20.7 (± 21.2)). The mean SBAC-L1 was 141.1 HU (± 45), 138.1 HU (± 44.8) and 154.8 HU (± 44.9) in the total, mSASSS ≥ 2 and mSASSS < 2 populations, respectively. Patients with bone bridges had lower SBAC-L1 than mSASSS ≥ 2 patients without ankylosis (p = 0.02) and more often SBAC-L1 ≤ 145 HU (73% vs 41.9%, p = 0.006). A SBAC-L1 ≤ 145 HU was not associated with structural spine involvement, but patients with bone bridges had significantly decreased SBAC-L1 and an increased probability of being under the fracture threshold.

Highlights

Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disorder with axial and peripheral involvement and sometimes some extra-articular events
Among 1503 spondyloarthritis patients followed between 2008 and 2017 and screened for biologic treatment, 73 patients fulfilled ankylosing spondylitis (AS) inclusion criteria, with a mean age of 60.3 years (± 10.7) and a large predominance of men (89%)
The prevalence of vertebral fracture (VF) was 12.3% in AS patients, and VF was mainly observed in mSASSS + patients (88.9%)

Summary

Introduction

Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disorder with axial (spinal and sacroiliac) and peripheral involvement (arthritis, enthesitis, dactylitis) and sometimes some extra-articular events (iritis, inflammatory bowel disease, dactylitis). The SBAC-L1 studied only trabecular bone in contrast to DXA, where bone formation (syndesmophytes, osteophytes...) or calcifications (vascular) may cause artefacts. This coefficient corresponded to the average bone mineral density, in Hounsfield units, of a region of interest (ROI), drawn in the trabecular bone, avoiding cortical bone. The diagnostic performance of SBAC-L1 was studied in rheumatoid arthritis In this population at risk of osteoporosis, 74% of patients with osteoporotic fractures were categorized as osteoporotic with a SBAC- L1 ≤ 135 HU, whereas only 42% were identified by DXA17. The SBAC-L1 measure seems to be an optimized method to study bone fragility of the trabecular bone in AS patients with spinal structural involvement, without the artefacts due to cortical bone or vascular calcifications, as with DXA10,13–15,19–22

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