title: Examining bone surfaces across puberty: a 20-month pQCT trial.
abstract: This follow-up study assessed sex differences in cortical bone growth at the tibial midshaft across puberty. In both sexes, periosteal apposition dominated over endosteal resorption. Boys had a greater magnitude of change at both surfaces, and thus, a greater increase in bone size across puberty. Relative increase in cortical bone area was similar between sexes.
  
  
  BACKGROUND
  Generally, sex differences in bone size become most evident as puberty progresses. This was thought to be caused, in part, by greater periosteal apposition in boys, whereas endosteal apposition prevailed in girls. However, this premise is based on evidence from cross-sectional studies and planar measurement techniques. Thus, our aim was to prospectively evaluate sex-specific changes in cortical bone area across puberty.
  
  
  METHODS
  We used pQCT to assess the tibial midshaft (50% site) at baseline and final (20 months) in girls (N = 68) and boys (N = 60) across early-, peri-, and postpuberty. We report total bone cross-sectional area (ToA, mm2), cortical area (CoA, mm2), marrow cavity area (CavA, mm2), and CoA/ToA ratio.
  
  
  RESULTS
  Children were a mean age of 11.9 +/- 0.6 (SD) years at baseline. At the tibia, CoA ranged from 230 +/- 44, 261 +/- 50, and 258 +/- 46 in early-, peri-, and postpubertal girls. In boys, comparable values were 223 +/- 36 (early), 264 +/- 38 (peri), and 281 +/- 77 (postpubertal). There was no sex difference for ToA or CoA at baseline. Increase in ToA and CoA was, on average, 10% greater for boys than girls across maturity groups. The area of the marrow cavity increased in all groups, but with considerable variability. The increase in CavA was significantly less for girls than boys in the early- and postpubertal groups. Change in CoA/ToA was similar between sexes across puberty.
  
  
  CONCLUSIONS
  Both sexes showed a similar pattern of change in CoA at the tibial midshaft, where periosteal apposition dominated over endosteal resorption. Boys showed a greater magnitude of change at both surfaces, and thus, showed a greater increase in bone size across puberty. The relative increase in cortical area was similar between sexes. These pQCT findings provide no evidence for endosteal apposition in postmenarchal girls.
authors.affiliation: Department of Orthopaedics, Faculty of Medicine, University of British Columbia, Vancouver, Canada.
authors.forename: Saija A
authors.initials: SA
authors.lastname: Kontulainen
authors.forename: Heather M
authors.initials: HM
authors.lastname: Macdonald
authors.forename: Karim M
authors.initials: KM
authors.lastname: Khan
authors.forename: Heather A
authors.initials: HA
authors.lastname: McKay
mesh_terms: D000293:Adolescent; D015519:Bone Density; D001846:Bone Development; D001842:Bone and Bones / Q000033:anatomy & histology / Q000502:physiology; D002648:Child; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D011627:Puberty / Q000502:physiology*; D012737:Sex Factors; D013977:Tibia / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000254:growth & development*; D014057:Tomography, X-Ray Computed