Consequences of spinal ankylosis on bone trabecular fragility assessed on CT scans in patients with ankylosing spondylitis. A retrospective study

Abstract

Background: Ankylosing spondylitis (AS) patients seems to be at risk of osteoporosis but bone screening is not often performed. The objective was to evaluate the effect of vertebral ankylosis on scanographic bone attenuation coefficient (SBAC) on lumbar vertebrae in AS patients. Patients and methods: This study included AS patients fulfilling New York criteria who underwent both thoraco-abdomino-pelvic computed tomography and X-rays during routine follow-up. The modified stoke ankylosing spondylitis spinal score (mSASSS) was scored on X-rays, and the presence of at least one syndesmophyte (mSASSS≥2) defined mSASSS+ patients. Ankylosis of a lumbar vertebra was defined by the presence of bone bridges to its two adjacent vertebrae. The SBAC was measured from L1 to L5, and the fracture threshold was set at SBAC£145 HU. Results: A total of 73 AS patients were included (mean age: 60.3 (±10.7) years, 65 men (89%)). Sixty patients (82.2%) were mSASSS+; 13 patients (17.8%) presented ankylosis of at least one lumbar vertebra. The SBAC of each lumbar vertebra was not significantly different between mSASSS-and mSASSS+ patients. The SBAC was lower for patients with at least one bone bridge than for patients without (p<0.05). Patients with lumbar vertebral ankylosis had a higher risk of presenting an SBAC≤145 HU (OR: 4.95 (95% CI: 1.1-17.4)). Conclusion: The presence of a bone bridge and complete ankylosis of lumbar vertebra were associated with a higher risk of SBAC under the fracture threshold, suggesting structural deterioration of trabecular bone in ankylosed vertebrae in AS patients.

Vertebral Bone Mineral Density, Vertebral Strength, and Syndesmophyte Growth in Ankylosing Spondylitis: The Importance of Bridging

“…Previous cross‐sectional studies that used QCT demonstrated that lower lumbar tBMD was associated with the presence of syndesmophytes (25,26), more extensive spinal changes (24), or bridging (10,23), but the proliferative changes in these studies were not restricted to the lumbar spine. Only Karberg et al (25) limited the examination of syndesmophytes to the lumbar spine, and only 2 studies adjusted for patient age (24,26).…”

“…Despite these commonalities, whether, and how, these processes are related is not well understood. It has been hypothesized that bridging syndesmophytes may promote bone loss by reducing vertebral mobility (10). However, 2 longitudinal studies have suggested the inverse, that low bone mineral density (BMD) predicts syndesmophyte formation (11,12).…”

“…To date, no study has utilized CT to measure both vertebral BMD and syndesmophytes. Previous studies in which BMD was measured using QCT relied on radiography for the detection of syndesmophytes (10,17,(22)(23)(24)(25)(26)(27). In the majority of studies, DXA has been used for BMD and radiography has been used for syndesmophytes (11,12,15,16,(28)(29)(30).…”

Osteoporosis in Inflammatory Arthritides: New Perspective on Pathogenesis and Treatment

“…Another recent study investigated the effect of vertebral ankylosis on scanographic bone attenuation coefficient (SBAC), measured from L1 to L5, in AS patients ( 105 ). It was found that patients with at least one bony bridge had lower SBAC values, while there was a correlation between the presence of full ankylosis and the probability of presenting SBAC ≤145 HU (fracture threshold), suggesting an impact of ankylosed vertebrae on trabecular bone deterioration.…”