Objective: The BoneXpert method for automated bone age determination from hand X-rays also determines the cortical thickness T and the bone width W in the three middle metacarpals. From these, the method derives the cortical area A=π W T (1 T/W), the metacarpal index MCI =A/(WW) and the Bone Health Index. Recently, the method has been extended down to new-borns, and the aim of this study is to report reference curves for these bone measures.
Method: 410 healthy children born in Paris in 1955 were followed with hand X-rays at ages 1, 3, 6, 9, 12 and 18 months, and then annually until age 20 years. Reference curves were defined versus bone age (BA) determined automatically on the Greulich Pyle scale, averaging over radius, ulna and 19 short bones.
Results: For males, the cortical thickness drops from 0.74 mm at BA 0.08 y to a minimum of 0.58 mm at BA 1.0, a reduction by 22%. Bone width increases by 38% from 3.2 to 4.4 mm in the same period, and cortical area grows by 19%. Bone length increases 43% from 16.6 to 24 mm. MCI drops from 0.55 to 0.37 (33%) and BHI from 4.8 to 3.4 (29%) in the same period. Females display a similar development, but their cortical thickness assumes its minimum at BA 0.9 y.
Conclusion: Infants exhibit a dramatic reconfiguration or bone geometry in the first year of life with strongly increasing width and length, and cortical thickness decreasing by 22%. MCI and BHI decrease in this period could it explain the increased fracture risk in children at age 1.0 compared to new-borns? (Hedström et al., Epidemiology of fractures in children and adolescents. Acta Orthop. 2010) surely, more studies are needed to assess the relationship between bone indices and fracture risk. The method could be more useful clinically than DEXA in infants, because (1) it is easier to record a hand X-ray, (2) the new reference curves provide Z-scores relative to the normal French population, and (3) the reference curves are expressed versus bone age rather than age.
Disclosure: HHT is owner and PT is employee of Visiana who develops the BoneXpert method for automated bone age and Bone Health Index determination.