Bone Abstracts

Objective: The aim of this study is to compare the bone health index (BHI) for healthy Swiss children born in 1955 with healthy Swiss children born a generation later.

Method: BHI is derived from the cortical thickness in the three middle metacarpals. It is determined with the BoneXpert medical device, which automatically analyses a standard bone age hand radiograph. The measurement result is independent of the sharpness of the image. The image data are from two longitudinal studies performed on healthy children at Zurich University Hospital. The first study recruited 232 children who were followed longitudinally with annual hand X-rays until age 20 years. The second study includes 200 children which have a participant in the first study as one of their parents, and these children were imaged biannually until adulthood.

Results: Reference curves of BHI are presented. The shapes of the curves are similar in the two generations, but the level of BHI is different. To quantify the level we form the average BHI over the bone age range 7–14 years for boys and 6–14 years for girls. This BHI level is found to be 1.5% lower in the modern generation.

Conclusion: The two generations exhibit the same adult height and the same tempo of maturation. In contrast, the BHI showed a secular trend of −1.5%. The stringent design of the study minimises other factors, which could explain the difference. Secular trends in bone health are difficult to study, because DEXA scanners were not available a generation ago, and even if they were, it would be difficult to ensure compatible calibration given the change of technology in these machines. In contrast, plain X-rays were a mature technology already 100 years ago, and large archives of hand X-rays have been collected for the purpose of bone age determination around the world and over the time. With the BHI method these become a valuable resource for studies of secular trends, population differences and relationship between children’s bone health and fracture incidence later in life.

Declaration of interest: H H Thodberg is the owner of Visiana, which holds and markets the BoneXpert medical device for automated determination of bone age. The other authors have nothing to disclose.