Unusually High Calcaneal Speed of Sound Measurements in Children with Small Foot Size

The purpose of this clinical note is to describe the performance of the Lunar Achilles Insight device in assessing bone quality at the calcaneus in 142 children between the ages of 5 and 11 y accessing healthcare in Johannesburg, South Africa. We observed an asymmetric bimodal distribution in speed of sound (SOS). The minor mode consisted of unusually high SOS values (≥1625 m/s), which were primarily observed among children with foot size <19 cm and height <119 cm. Cortical regions of the bone may have been inadvertently included in the region of interest for smaller feet, causing unusually high SOS values. The unusually high SOS values indicate that the validity of SOS in this device, as it is currently used for measuring bone quality in young children, is questionable. Future studies using this device in young children should develop new methodology to account for smaller foot size.