A fracture in childhood is associated with low bone mineral density (BMD), but it is debated whether a fracture at growth also predicts low BMD in young adulthood. The purpose of this work was to gender-specifically evaluate whether children with a fracture are at increased risk of low BMD in young adulthood. Distal forearm BMD (g/cm 2 ) was measured with single-photon absorptiometry (SPA) in 47 boys and 26 girls (mean age 10 years, range 3-16 years) with an index fracture and in 41 boys and 43 girls (mean age 10 years, range 4-16 years) with no fracture. BMD was re-measured mean 27 years later with the same SPA apparatus and with dual-energy absorptiometry (DXA), quantitative ultrasound (QUS), and peripheral computed tomography (pQCT). Individual Z-scores were calculated using the control cohort as reference population. Data are presented as means with 95% confidence intervals (95% CI) within brackets and correlation with Pearson's correlation coefficient. Boys with an index fracture had at fracture event a distal forearm BMD Z-score of À0.4 (95% CI, À0.7 to À0.1) and at follow-up À0.4 (95% CI, À0.7 to À0.1). Corresponding values in girls were À0.2 (95% CI, À0.5 to 0.1) and À0.3 (95% CI, À0.7 to 0.1). The deficit in absolute bone mass was driven by men with index fractures in childhood due to low energy rather than moderate or high energy. There were no changes in BMD Z-score during the follow-up period. The BMD deficit at follow-up was in boys with an index fracture verified with all advocated techniques. A childhood fracture in men was associated with low BMD and smaller bone size in young adulthood whereas the deficit in women did not reach statistical significance. ß

Cross-sectional studies suggest that premature birth and low birth weight may both be associated with low peak bone mass. We followed bone traits in preterm individuals and controls for 27 years and examined the effects of birth weight relative to gestational age [stratified as small for gestational age (SGA) or appropriate for gestational (AGA)] on adult bone mineral density (BMD). We measured distal forearm BMC (g/cm) and BMD (g/cm(2)) with single-photon absorptiometry (SPA) in 46 preterm children (31 AGA and 15 SGA) at mean age 10.1 years (range 4-16) and in 84 healthy age-matched children. The measurements were repeated 27 years later with the same SPA apparatus but then also with dual energy absorptiometry and peripheral computed tomography (pQCT). Preterm individuals were shorter (p = 0.03) in adulthood than controls. Preterm AGA individuals had similar BMC and BMD height-adjusted Z-scores in adulthood compared to controls. Preterm SGA individuals had lower distal forearm BMC and BMD height-adjusted Z-scores in adulthood than both controls and preterm AGA individuals. Preterm SGA individuals had lower gain from childhood to adulthood in distal forearm BMC height-adjusted Z-scores than controls (p = 0.03). The deficits in preterm SGA individuals in adulthood were also captured by DEXA in height-adjusted femoral neck (FN) BMC Z-score and height-adjusted FN BMD Z-score and by pQCT in tibial cross-sectional area (CSA) Z-score and stress strain index (SSI) Z-score, where all measurements were lower than controls (all p values <0.05). Preterm SGA individuals are at increased risk of reaching low adult bone mass, at least partly due to a deficit in the accrual of bone mineral during growth. In our cohort, we were unable to find a similar risk in preterm AGA individuals.

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