Assessment of Spine Bone Mineral Density in Juvenile Idiopathic Arthritis: Impact of Scan Projection

Although children with juvenile idiopathic arthritis (JIA) are at risk for vertebral fractures, recent conventional posterior-anterior (PA) spine dual-energy X-ray absorptiometry studies reported minimal areal bone mineral density (aBMD, g/cm2) deficits. Width-adjusted BMD (WA-BMD, g/cm3) represents the bone mineral content (BMC) from the lateral projection, excluding the dense cortical spinous processes, divided by the estimated vertebral body volume based on paired PA-lateral bone dimensions. Therefore, WA-BMD may be more sensitive to JIA effects on the predominantly trabecular vertebral body. Age- and sex-specific Z-scores for spine aBMD and WA-BMD were generated in 84 JIA subjects compared with healthy controls, aged 5-21 yr. JIA was associated with lower mean WA-BMD Z-scores (−0.78, 95% CI: −1.03, −0.53; p < 0.001) and aBMD Z-scores (−0.26, 95% CI: −0.49, −0.02; p < 0.05), compared with controls. WA-BMD Z-scores were significantly lower than aBMD Z-scores in JIA (p < 0.001). A significant JIA by age interaction (p < 0.001) indicated that the magnitude of the difference between WA-BMD and aBMD Z-scores was greater in younger subjects. In conclusion, WA-BMD may be more sensitive to disease effects in children because it selectively measures the trabecular-rich vertebral body and is independent of growth-related changes in BMC of the dense spinous processes.