Interpretation of paediatric bone evaluation by dual-energy x-ray absorptometry (dxa)

The use of DXA in children requires an understanding of the contribution of allometry in bone development, to enable accurate assessment of current/future fracture risk.   The aims of this thesis were to determine the roles of gender and ethnicity in bone mass acquisition and to investigate whether reference data, which accounted for variations in bone and body size, improved the diagnostic ability of DXA. In healthy children there was a strong correlation between muscle and bone mass, modulated by bone length and body fat.  Ethnic differences affected skeletal geometry; Black children had shorter wider bones than Asian children, with White children having the longest narrowest bones.  The most significant non-mechanical influence on bone was oestrogen, highlighted by the sexual dimorphism in the muscle-bone relationship observed during late puberty. The generation of the first ethnic and gender-specific, size adjusted, UK reference data was used to review different size adjustment techniques, for the assessment of bone fragility in a group of chronically sick children.  All improved the specificity of DXA for predicting fracture but no single technique was better than another.  Size-adjusted bone mass was relatively sensitive and specific at identifying vertebral fractures.  However, whilst DXA was poor at discriminating long bone fracture, it may provide insight into the etiology of reduced bone mass.  This study will help to uncover potential pathways for intervention and thus the prevention of osteoporosis and fragility fractures in childhood and adult life.