Bone Abstracts

Bone accrual and the attainment of peak bone mass influence an individual’s predisposition to fracture or osteoporosis later in life. The developmental tempo and the movement of the periosteal and endosteal surfaces of the appendicular skeleton during growth result in variations in bone mineral content and density. During puberty the differential in peak height and peak bone mass accretion negatively influence bone strength. A surrogate measure of bone strength is the metacarpal index (MI) which has been shown to predict fracture risk in adults. This longitudinal study describes the differences in the metacarpal bones from pre-puberty through adolescence by ethnicity and gender. 689 subjects from the South African (SA) Birth to 20 Cohort were studied annually between 9 and 22 years of age. Radiogrammetry was performed on 4590 hand-wrist x-rays of black and white boys and girls. Total bone length (L), and cortical and medullary width were measured at the midshaft of the second metacarpal using digital vernier callipers calibrated to two decimal places. The MI was derived by dividing the combined cortical thickness by total bone width (W). Cross-sectional statistical analysis (t-test) showed no ethnic differences in L and W at all ages. Compared to boys, black and white girls had significantly lower L from 14–20 years and narrower W at all ages (P<0.05). Data were not adjusted for height. In both black boys and girls the MI was lower than in their white peers indicative of lower cortical thickness relative to bone width in black children (P<0.05). Comparison of the MI by gender showed that at all ages black girls had a greater MI than boys, however, in white children a significant gender difference was only present between the ages of 10 and 14 years (P<0.05). The lower MI in black boys and girls conflicts with the lower prevalence of fracture rates reported in black SA adults and children compared to their white counterparts. Differences in metacarpal dimensions are suggestive of ethnic and gender disparities in bone mass accrual in SA children from pre-puberty through adolescence.

Disclosure: The authors declared no competing interests.