Objective: The forearm is a common fracture site during childhood, but DXA pediatric reference data for areal bone mineral density (aBMD) at the ultradistal (UD) radius are lacking. The objective of this study was to first, develop age-, sex-, and ancestry-specific reference data for UD radius aBMD; second, assess the relationship between UD radius aBMD and a) other DXA aBMD measures and b) radius bone volumetric density and geometry by pQCT; and third, examine the tracking of UD radius aBMD over time.
Methods: Data were acquired from the multi-site, longitudinal, Bone Mineral Density in Childhood Study (n=2014, 922 males, 22% African American) of healthy children ages 519 years at baseline, who provided >10,000 annual DXA measurements over 6 years. In a subset of our cohort (n=144), distal radius pQCT scans were acquired at the 3% and 30% sites relative to the distal growth plate. Reference data for UD radius aBMD were generated using the LMS method. Relationships between UD radius aBMD and age, sex, population ancestry, and other bone measures were assessed using mixed effects regression and partial correlations. Tracking from baseline to the 6-year time point was assessed using Pearsons correlations.
Results: UD radius aBMD increased non-linearly with age and was greater in African Americans and males (all P<0.001). Age-, sex-, and ancestry-specific UD radius aBMD reference curves were constructed and used to calculate Z-scores. UD radius aBMD Z-scores correlated positively with total body, lumbar spine, total hip, femoral neck, and distal 1/3 radius aBMD Z-scores (r=0.56 to 0.64, all P<0.001). Partial correlations (accounting for age, age2, gender and African American ancestry) between UD radius aBMD and pQCT measures of total and trabecular volumetric density were r=0.53 and 0.45, (P<0.001) respectively. Furthermore, UD radius aBMD Z-scores tracked strongly over 6 years (r=0.69, all P<0.05).
Conclusion: This study provides the first pediatric reference dataset for UD radius aBMD. In contrast to other DXA measures, the UD radius is an appendicular skeletal site comprised of mostly trabecular bone. Given these unique characteristics, UD radius aBMD might provide valuable insight in the clinical setting.
Disclosure: The authors declared no competing interests.