Several studies in ALSPAC have revealed significant effects of different factors on bone size as assessed by DXA measurements. Interestingly, effects such as social position persist after adjustment for height, suggesting an influence on bone width (1). This observation is important, since influences on bone width imply that bone shape and geometry are being affected, which may have important implications for the risk of sustaining osteoporotic fractures in later life. Therefore, we are keen to explore potential influences on bone geometry in ALSPAC in more detail.

Initial time constraints in the focus clinics limited the acquisition of all three bone scans (Total body and Hip DXA, and PQCT) mainly due to the unfamilarity of the PQCT scanner, therefore we were limited to using only total body DXA and PQCT. However now the operators have become more familiar with the PQCT scanner the length of time required complete this section has been reduced. Therefore at the end of, and breaks in each clinic session there is now time to perform a unilateral hip DXA scan.

Currently total body DXA scans are being performed, and although total body DXA provides important information about bone density in the body it does not provide any information about the shape and strength of the bone. Other groups are currently measuring physical activity within the cohort and it is postulated that bone adapts to the functional requirements placed upon it. The hip is a key area linking the peripheral and axial skeleton together, and due to the geometric orientation of the hip functional stress and strains are very large, and therefore have the potential to show the greatest adaptation to these stresses and strain.

We are currently investigating the effects of physical activity on bone shape and geometry using pQCT as part of a welcome grant. However pQCT is confined to the use of the peripheral skeleton and we can only measure the tibia. Whilst the information gained from this part of the investigation is important due to the direct measurement of shape and geometry, it can not be used to infer information about the hip. Although hip DXA does not directly measure geometry unlike the pQCT, these parameters can be estimated, therefore we are keen to incorporate this scan into the current clinic, especially as there are no extra associated costs incu

We would like to include a unilateral hip DXA, time permitting, in the densitometry element of the data collection clinic. We are proposing to perform all 3 scans in the Age 17 clinic, and have previously collected information on hip geometry at age 13/14. By collecting hip geometry information at age 15/16 we will be better able to investigate the growth and development of bone whilst the young people are going through puberty, and how this may influence osteoporotic fractures later in life.

Hip DXA uniquely estimates the strength and cross sectional area of the hip, this aspect of bone geometry cannot be obtained via the PQCT or the total body DXA. The hip is commonly associated with osteoporotic fractures later in life and th