The correlation between dual-energy X-ray absorptiometry measures of bone density in the proximal femur and lumbar spine of children

Objective. To assess the correlation between a pediatric patient's proximal femur and lumbar spine bone mineral density (BMD) Z-scores, and the side-to-side difference between proximal femurs. Design. Three hundred and thirty-nine patients aged 2.2-17.0 years with an assortment of underlying conditions underwent dual-energy X-ray absorptiometry (DXA) measures of BMD in both proximal femurs and the lumbar spine. Results. Z-scores in the proximal femur and lumbar spine correlated highly (r=0.73, P=0.0001), but for individual patients the difference was often significant, and increased as BMD deviated further from normal. For patients with proximal femur Z-scores of 1 to -1 the mean difference between proximal femur and lumbar spine Z-scores was 0.5; with proximal femur Z-scores of less than -3 the mean difference was increased to 1.7. In conditions which symmetrically involve the lower extremities, the right and left proximal femur Z-scores differed on average by only 0.2. Conclusion. BMD measurements for pediatric patients are most easily interpreted by clinicians if converted to Z-scores, yet these are usually available only for the lumbar spine. Age-normalized BMD assessment at more than one site is necessary to provide a more reliable, complete assessment of bone mineral status in pediatric patients.