Ankylosing spondylitis (AS) is a chronic inflammatory disease of the spine characterized among other features by spinal boney proliferation, back pain, loss of flexibility, and increased fracture risk. Overlying bone limits the utility of bone mineral density (BMD) by dual X-ray absorptiometry (DXA) in the spine. Trabecular bone score (TBS) is a bone texture measurement derived from the spine DXA image that indicates bone quality and fracture risk independent of BMD.
Using the Manitoba Bone Density Program database, patients with diagnosis codes for ankylosing spondylitis, baseline DXA and lumbar spine TBS were identified. Incident nontraumatic fractures (major osteoporotic [MOF], clinical spine, hip, and all fracture) were identified from population based databases. Cox-proportional hazard models are presented.
We identified 188 patients with diagnosed AS. TBS was lower in those with incident MOF (1.278 ± 0.126, compared to 1.178 ± 0.136, p < 0.001). Unadjusted TBS and FRAX-MOF-BMD adjusted predicted major osteoporotic fracture (N = 19) (hazard ratio [HR] 2.04, 95% confidence interval [CI]: 1.28-2.26, p = 0.003; HR 1.81, 95% CI: 1.11-2.96, p = 0.018). TBS unadjusted and FRAX-MOF-BMD adjusted also predicted clinical spine fracture (N = 7) (HR 2.50, 95% CI: 1.17-5.37; p = 0.019; HR 2.40 95% CI: 1.1-5.25; p = 0.028). Higher HRs were observed for prediction of hip fracture (N = 6), but these did not achieve statistical significance (FRAX-adjusted HR 1.74, 95% 0.73-4.17; p = 0.211). Unadjusted models show TBS was predictive of all fracture (N = 27) (HR 1.60, 95% CI: 1.08-2.39; p = 0.020), which was borderline significant after adjustment for FRAX-MOF-BMD (HR 1.51, 95% CI: 1.00-2.29; p = 0.052).
We report the first analysis of TBS for fracture prediction as an incident event in AS. TBS independently predicted major osteoporotic and clinical spine fracture in AS independent of FRAX.