Bone Abstracts

The impact of sex and maturation on trabecular (Tb) and cortical (Ct) microarchitecture in children and young adults has not been well established. The new second-generation high-resolution peripheral quantitative CT (HR-pQCT) scanner (XCT II, Scanco Medical) incorporates three important advances to provide greater spatial resolution, direct measures of Tb thickness and spacing and measures in the Ct midshaft. The aim of this study was to identify sex and maturation effects on bone microarchitecture and to determine the impact of adjustments for IGF1 and leg muscle mass (LM) by DXA. This cross-sectional study included 286 healthy participants (148 females), ages 5 to 30 yrs recruited from the community and excluded from diseases or medications known to effect growth and bone health. The reference line was placed 2 mm proximal to the proximal margin of the growth plate (or growth plate remnant if fused) and scans were centered 3.5% (distal site) and 30% (proximal site) of tibia length proximal to the reference line. Log linear regression models were adjusted for age, age2, sex, tibia length and Tanner stage. At the proximal site, female participants had significantly greater Ct bone mineral density (BMD) and lower Ct thickness and porosity compared with males. Greater skeletal maturity was associated with greater Ct thickness, area and BMD independent of age and sex. Cortical porosity was markedly higher in pre-pubertal participants (an average of 5.3 and 4.0% in Tanner 1 males and females respectively, compared with 1.4 and 1.0% in Tanner 5). In the tibia metaphysis, greater maturation was associated with greater Tb thickness and the maturation effects were significantly more pronounced in males (significant sex-Tanner interaction). Tb number did not differ with maturation in males or females. After adjustment for IGF1 the sex and Tanner stage effects persisted and IGF1 was also positively correlated to trabecular number and thickness and cortical thickness and area at the proximal site. However, adjustment for LM eliminated sex and Tanner stage differences in these outcomes. In conclusion, the new XCT II device captures sex and maturation effects that were not evident with prior technology.

Disclosure: Andrew Burghardt’s institution, UCSF, has research support by ultragenyx. Kyla Kent is a consultant for Ascendis Pharmaceuticals.