Opportunistic use of dual-energy X-ray absorptiometry to evaluate lumbar scoliosis.

Abstract

Osteoporosis and scoliosis are interrelated disease processes. Dual-energy X-ray absorptiometry (DXA), used to assess bone density, can also be used to evaluate spinal deformity since it captures a posteroanterior (PA) image of the lumbar spine. We assessed the use of DXA to evaluate lumbar spine alignment. A lumbar spine DXA phantom was used to assess the effects of axial and sagittal plane rotation on lumbar bone mineral content (BMC), density (BMD), and L1-L4 Cobb angle measurements. Using two subject cohorts, intra- and inter-observer reliability and validity of using DXA for L1-L4 Cobb angle measurements in the coronal and sagittal planes were assessed. Axial and sagittal plane rotation greater than 15° and 10°, respectively, significantly reduced measured BMD and BMC; there was minimal effect on Cobb angle measurement reliability. In human subjects, excellent intra- and inter-observer reliability was observed using lumbar PA DXA images for Cobb angle measurements. Agreement between Cobb angles derived from lumbar PA DXA images and AP lumbar radiographs ranged from good to excellent. The mean difference in Cobb angles between supine lumbar PA DXA images and upright AP lumbar radiographs was 2.8° in all subjects and 5.8° in those with scoliosis. Lumbar spine rotation does not significantly affect BMD and BMC within 15° and 10° of axial and sagittal plane rotation, respectively, and minimally affects Cobb angle measurement. Spine alignment in the coronal plane can be reliably assessed using lumbar PA DXA images.