Chapter 42 Chapter 42 Bone Acquisition in Adolescence Copyright © 2013 Elsevier Inc. All rights reserved.

FIGURE 42.1 Percentage of adult bone mineral content accrual within 1-year biological age categories (years from peak height velocity (PHV)) For the total body for (A) boys and (B) girls. Bars represent mean and 95% confidence intervals. Source: modified from Baxter-Jones et al. [32] with permission from Wiley. 2

Copyright © 2013 Elsevier Inc. All rights reserved. FIGURE 42.2 A schematic representation of differences in total bone size and cortical bone mineral density for girls (G) and boys (B) across puberty (assessed using self-report Tanner staging (T)). Tanner stage 1 is defined as prepuberty (PRE), Tanner stages 2 and 3 as early puberty (EARLY), Tanner stage 4 as peripuberty (PERI), and Tanner stage 5 as postpuberty (POST). Significant differences between boys and girls are shown for bone strength (failure load) estimated with finite element analysis of high-resolution peripheral quantitative computed tomography (HR-pQCT) scans. Boys' values exceed girls' values after early puberty, and cortical porosity (Ct.Po) was greater in boys than girls after prepuberty. Diagram not to exact scale. Source: reproduced from Nishiyama et al. [62] with permission from Wiley. 3

Copyright © 2013 Elsevier Inc. All rights reserved. FIGURE 42.3 Illustration of the opposite effects of increases in bone width and bone length on bone bending strength. The two rods on the left have the same length, but the larger rod has twice the diameter of the thinner rod; therefore, bone-bending strength is eight times greater in the larger rod. The two rods on the right have the same diameter, but a doubling of the rod length decreases bone strength to one-eighth of the original value. Source: reproduced from Rauch [72] with permission. 4

Copyright © 2013 Elsevier Inc. All rights reserved. FIGURE 42.4 A functional model of bone development based on the mechanostat theory [94] and related approaches [9]. The central component of the regulation of bone development and adaptation is the feedback loop between bone deformation (tissue strain) and bone strength. During growth, this homeostatic system must continually adapt to external challenges (increases in bone length and muscle force) to keep tissue strain close to a preset level (setpoint). Various modulating factors influence aspects of the regulatory system as indicated by the dashed arrows. Source: adapted from Rauch and Schoenau [9] and reproduced from [182] with permission from Future Medicine Ltd. 5

Copyright © 2013 Elsevier Inc. All rights reserved. FIGURE 42.5 Tissue velocity curves for lean tissue mass, cross-sectional area (A) and section modulus (B) at the narrow neck region of the proximal femur aligned by maturation. The maturational age of 0 represents the age at peak height velocity (12.49 years (y)). The solid drop-down lines landmark the maturation age at which the peak tissue velocities occurred. *Indicates a significant difference between the age of peak lean tissue velocity (PLTV) and peak cross-sectional area velocity. **Indicates a significant difference between PLTVand peak section modulus velocity. Source: reproduced from Jackowski et al. [145] with permission from Elsevier. 6

Copyright © 2013 Elsevier Inc. All rights reserved. FIGURE 42.6 Relationship between 16-month change in estimated bone strength (polar strength strain index, SSI p ; by peripheral quantitative computed tomography (pQCT)) and change in total body lean mass (by dual- energy X-ray absorptiometry (DXA)) (A; r = 0.70, p < 0.01) and change in total body fat mass (by DXA) (B; r = 0.06, p = 0.22) in overweight (triangles) and healthy weight (squares) boys (dark) and girls (light). Source: reproduced from Westzeon et al. [158] with permission from Wiley. 7

Copyright © 2013 Elsevier Inc. All rights reserved. FIGURE 42.7 Average side-to-side differences in humeral midshaft total bone cross-sectional area (CSA), cortical CSA, cortical bone mineral density (BMD), and bone strength index (BSI) between the playing and nonplaying arm in female racquet sport athletes as measured with peripheral quantitative computed tomography (pQCT). The solid line represents the playing arm (or dominant arm in controls). Source: adapted from Daly [178] and Kontulainen et al. [190] and reproduced from Macdonald et al. (Macdonald HM, Burrows M, McKay HA. Physical Activity and Skeletal Growth in Osteoporosis in Men, 2nd edition 2010, Orwoll ES, Bilezikian JP, Vanderschueren D, eds., pp. 131–146. Academic Press, San Diego, CA) with permission from Elsevier 8