The differing tempo of growth in bone size, mass, and density in girls is region-specific

Abstract

The differing tempo and direction of growth of the periosteal and endocortical surfaces, and the differing tempo of growth of the axial and appendicular skeleton, may predispose to regional deficits in bone size, bone mineral content (BMC), and volumetric bone mineral density (vBMD). These traits were measured during 2 years by dual x-ray absorptiometry in 109 girls. By 7 years of age, bone size was approximately 80% of its maturational peak, and BMC was approximately 40% of its peak. Before puberty, the legs grew more rapidly than the trunk. During puberty, the growth spurt was truncal. Between 7 and 17 years, femoral and lumbar spine BMC increased by 50-150% because bone size increased. vBMD increased by 10-30%. Thus, growth builds a bigger, but only moderately denser, skeleton. Regions growing rapidly, or distant from their peak, may be more severely affected by illness than those growing slowly or nearer completion of growth. Depending on the age of exposure to disease, deficits may occur in limb dimensions (prepuberty), spine dimensions (early puberty), or vBMD by interference with mineral accrual (late puberty). As vBMD is independent of age before puberty, the position of an individual's vBMD in the population distribution is established early in life. Bone fragility in old age may have its foundations in growth.

Figure 1

Height, regional lengths, and total body and regional BMC expressed as a percentage of the predicted young adult peak value versus bone age. The shaded area represents the pubertal growth period (Tanner stage 2 to menarche).

Figure 2

The bone-age adjusted residuals for spine and leg BMC increased with advancing age, whereas the bone age adjusted residuals for sitting height and leg length did not. Prepubertal (open circles), peripubertal (filled circles), and postpubertal (filled diamond symbols).

Figure 3

Rates of growth in regional bone length (centimeters per month) and bone mass (grams per month) versus bone age (mean ± SEM). The shaded area represents the pubertal growth period (Tanner stage 2 to menarche).

Figure 4

Midshaft metacarpal and femoral dimensions and femoral midshaft vBMD and cortical true BMD as a function of pubertal status.

Figure 5

BMC and vBMD at the femoral midshaft and third lumbar vertebra versus bone age.

Figure 6

Serum bone specific alkaline phosphatase, osteocalcin, collagen propeptide of type I collagen (PICP), and urinary type I C-telopeptide breakdown products (CrossLaps) versus bone age. Prepubertal (filled circles), peripubertal (open circles), and postpubertal (crosses).

Figure 7

Serum bone specific alkaline phosphatase, osteocalcin, collagen propeptide of type I collagen (PICP), and urinary type I C-telopeptide breakdown products (CrossLaps) versus estradiol. Numbers denote maturational stages; 1 (Tanner stage 1), 2 (includes Tanner stages 2–4), 3 (1.0 ± 0.1 years after menarche), and 4 (3.7 ± 0.1 years after menarche).