Forearm length measurement errors affect pediatric BMD

Abstract:

Placement of the region of interest (ROI) for analysis of a standard forearm dual x-ray absorptiometry (DXA) scan requires a precise forearm length measurement, as placement of the ROI affects the bone mineral density (BMD) results of the scan. In longitudinal pediatric studies, this is potentially a major source of error because subjects are still growing. To determine if inaccuracy of forearm length measurement has an impact on the BMD results of the radius and to compare this to reference forearm growth rate, we studied forearm DXA scans from 1554 children, ages 6 to 16, (863 girls) who were enrolled in BMDCS at 5 clinical centers. Each subject had a baseline and a one year follow-up scan of the forearm on the Hologic Delphi. Forearm length measurements were obtained at each visit. We found that the cross-sectional growth rate in forearm length is similar between boys and girls, with a steady increase of about 9mm/year till age 10, after which the mean growth rate declines. The longitudinal change rate at 3 study sites followed a similar pattern as the cross-sectional changes. The remaining two sites showed one with significantly higher growth rate and the other with a negative growth rate. 34 of those scans were chosen for reanalysis after intentionally shortening the original forearm length by 10 mm. The change in BMD between the original and shortened length data was 0.9 and 1.5% for the mid and total radii, respectively (p<0.05). These data demonstrate normal forearm lengths versus age and shows that measurements of BMD are clinically insensitive to minor errors in forearm length.

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