Analysis of proximal femur DXA scans in growing children: Comparisons of different protocols for cross-sectional 8-month and 7-year longitudinal data

Dual-energy X-ray absorptiometry (DXA) is a widely used method for measurin g bone mineral in the growing skeleton. Because scan analysis in children o ffers a number of challenges, we compared DXA results using six analysis me thods at the total proximal femur (PF) and five methods at the femoral neck (FN), In total we assessed 50 scans (25 boys, 25 girls) from two separate studies for cross-sectional differences in bone area, bone mineral content (BMC), and areal bone mineral density (aBMD) and for percentage change over the short term (8 months) and long term (7 years). At the proximal femur f or the short-term longitudinal analysis, there was an approximate 3.5% grea ter change in bone area and BMC when the global region of interest (ROI) wa s allowed to increase in size between years as compared with when the globa l ROI was held constant. Trend analysis showed a significant (p < 0.05) dif ference between scan analysis methods for bone area and BMC across 7 years. At the femoral neck, cross-sectional analysis using a narrower (from defau lt) ROI, without change in location, resulted in a 12.9 and 12.6% smaller b one area and BMC, respectively (both p < 0.001), Changes in FN area and BMC over 8 months were significantly greater (2.3 %, p < 0.05) using a narrowe r FN rather than the default ROI, Similarly, the 7-year longitudinal data r evealed that differences between scan analysis methods were greatest when t he narrower FN ROI was maintained across all years (p < 0.001), For aBMD th ere were no significant differences in group means between analysis methods at either the PF or FN, Our findings show the need to standardize the anal ysis of proximal femur DXA scans in growing children.