Bone Abstracts

Skeletal development during childhood and adolescence is an important determinant of adult bone health. Patterns of growth differ between populations, but it is unclear how these differences relate to changes in bone size and volumetric density. We aimed to examine ethnic differences in skeletal phenotype in the context of pubertal growth and development in 279 adolescent males from Johannesburg, South Africa.

We performed annual peripheral quantitative computed tomography (pQCT) at the 38% tibial site between the ages of 12.3 and 22.2 years. Outcome measures were volumetric bone mineral density (vBMD) and cortical cross-sectional area (CSA). Changes in each bone parameter and height were modelled longitudinally using superimposition by translation and rotation (SITAR),¹ stratified by ethnicity. The age at peak velocity (APV) was estimated from the individual growth curves, and these ages were compared within and between groups using two-sample t-tests.

Mean height APV was 13.7 (S.D. 1.0) years in black males and 12.7 (0.8) years in white males (difference P<0.01). Mean APV for cortical CSA was 13.2 (1.1) and 12.9 (0.8) years respectively (P=0.06). Peak changes in cortical CSA preceded the pubertal growth spurt by an average of 6 months in black males, but occurred 3 months after peak height growth in white males. Mean APV for vBMD was 14.8 (1.2) years in black males and 14.0 (1.0) years in white males (P<0.01), an average of 13 and 16 months after peak height velocity respectively. Changes in vBMD during growth could represent reduced bone turnover or infilling of the Haversian systems.

The delay between peak changes in cortical CSA and vBMD suggests a period of consolidation during which mineral is deposited primarily within the existing cortical envelope rather than only on the bone surfaces. The mean delay was significantly longer among black males (19 months) than among white males (13 months) (P<0.01). This may reflect ethnic differences in mineral metabolism, or may be related to differing environmental influences such as nutrition and physical activity. These possible determinants of timing in skeletal growth will require further investigation, as will the implications for adult bone health.

Disclosure: The authors declared no competing interests.

Funding: SA Medical Research Council; Wellcome Trust; National Research Foundation; UK Medical Research Council and Department for International Development under the MRC/DFID Concordat agreement (MRC programme U105960371); Bone Research Society Barbara Mawer Travelling Fellowship.

Reference: 1. Cole T et al. Int J Epidemiol 2010 39 1558–1566.