title: Sex differences in trabecular bone microarchitecture are not detected in pre and early pubertal children using magnetic resonance imaging.
abstract: BACKGROUND
  Sex differences in trabecular bone microarchitecture have been reported in adults and adolescents, but studies in children are lacking. The primary aim of this study was to determine if there are sex differences in magnetic resonance imaging (MRI)-based measures of trabecular bone microarchitecture at the distal femur of children.
  
  
  METHODS
  Pre and early pubertal boys (n=23) and girls (n=20) between the 5th and 95th percentiles for height, body mass and BMI were studied. Apparent trabecular bone volume to total volume (appBV/TV), trabecular number (appTb.N), trabecular thickness (appTb.Th), trabecular separation (appTb.Sp) and a composite measure of trabecular bone microarchitecture (TBMcom) were assessed at the lateral aspect of the distal femur using MRI. Areal bone mineral density (aBMD), bone mineral content (BMC) and bone area were assessed at the distal femur using dual-energy X-ray absorptiometry (DXA). Tanner staging was used to assess pubertal development. Physical activity was assessed using an accelerometry-based activity monitor. Calcium intake was assessed using diet records.
  
  
  RESULTS
  There were no sex differences in age, height, femur length, body mass, physical activity or calcium intake (all P>0.05). There were no sex differences in any MRI-based measure of trabecular bone microarchitecture. Consistent with the MRI-based measures, there were no differences in aBMD, BMC or bone area from DXA at the distal femur (P>0.05). appBV/TV, appTb.N, appTb.Th, appTb.Sp and TBMcom were also moderately to strongly related to aBMD (r=0.73, 0.63, 0.51, -0.74 and 0.61, respectively, p<0.001) and BMC (r=0.84, 0.63, 0.66, -0.80 and 0.77, respectively, P<0.001).
  
  
  CONCLUSIONS
  The findings suggest that there are no differences in measures of trabecular bone microarchitecture at the distal femur of pre and early pubertal boys and girls who are similar in size, physical activity and calcium intake. Future studies with larger sample sizes that cover all pubertal stages are needed to determine if sex differences in trabecular bone microarchitecture emerge at the distal femur and other weight bearing bone sites.
authors.affiliation: Department of Kinesiology and Applied Physiology, University of Delaware, Newark, DE 19716, USA. modlesky@udel.edu
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Modlesky
authors.forename: Deepti
authors.initials: D
authors.lastname: Bajaj
authors.forename: Joshua T
authors.initials: JT
authors.lastname: Kirby
authors.forename: Brianne M
authors.initials: BM
authors.lastname: Mulrooney
authors.forename: David A
authors.initials: DA
authors.lastname: Rowe
authors.forename: Freeman
authors.initials: F
authors.lastname: Miller
mesh_terms: D015502:Absorptiometry, Photon; D015992:Body Mass Index; D015519:Bone Density; D001842:Bone and Bones / Q000033:anatomy & histology*; D002648:Child; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011627:Puberty; D012737:Sex Factors