Assessment of skeletal maturation in infants: comparison between two methods in hypothyroid patients

Conventional skeletal radiography is the standard technique for assessing skeletal age. However, radiography cannot demonstrate cartilage and is therefore of lesser value in infancy when the ossification centres are composed mainly of cartilage. By comparison, US clearly demonstrates cartilage and bone.

In the present study, we compared radiography and sonography for the assessment of skeletal age in neonates and infants.

Because delayed skeletal maturation is a feature of congenital hypothyroidism and assessment of skeletal age is routinely performed in our centre, we studied 55 hypothyroid infants (aged 7-66 days). AP radiographs and sonograms, acquired using high-frequency scanners, were obtained and dimensions of the distal femoral epiphyseal ossification centre (DFE) were compared.

Measurements of DFE by the two methods showed excellent correlation (R = 0.94, P = 0.0001). Radiographs did not demonstrate a DFE in 11 infants, and US did not show it in 6. In no infant did radiography demonstrate DFE not seen by US. Moreover, DFE dimensions on US were larger than those measured on radiographs. Infants with absent thyroid gland had a DFE significantly smaller than those infants with ectopic or normally placed glands (P < 0.001), on both radiographs and sonograms.

Our data suggest that sonography is a valid alternative to standard radiography for the assessment of skeletal age in infants.