title: Walking age does not explain term versus preterm difference in bone geometry.
abstract: OBJECTIVE
  To elucidate the relationship between bone geometry and onset of walking in former term and preterm children.
  
  
  METHODS
  We conducted a cross-sectional study of 128 preschool children aged 3 to 5 years who underwent peripheral quantitative computerized tomography measures of bone size at the distal tibia. Linear models were developed, stratifying by sex, to determine whether bone differences between children born term and preterm were caused by differences in walking age.
  
  
  RESULTS
  Children with a history of preterm birth walked later than children born at term (12.4 +/- 0.5 versus 10.9 +/- 0.2 months; P = .004); however, gestation-corrected walking age (11.4 +/- 0.5 for children born preterm) did not differ. In multiple regression analysis, boys born preterm had larger periosteal and endosteal circumferences and smaller cortical thickness and area than boys born term (least square means, 49.7 +/- 1.3 mm, 43.0 +/- 1.8 mm, 1.1 +/- 0.11 mm, and 49.3 +/- 3.2 mm2 versus 47.0 +/- 0.5 mm, 38.5 +/- 0.7 mm, 1.4 +/- 0.04 mm, and 56.9 +/- 1.2 mm2, respectively; all P < .05). Preterm birth remained statistically significant after adding the age of walking to the models, but no longer significant when current activity levels were included.
  
  
  CONCLUSIONS
  Greater periosteal and endosteal circumferences, with smaller cortical bone thickness and area, were found in former preterm boys, but not girls, and were explained by differences in current activity levels, not age of walking.
authors.affiliation: EA Martin Program in Human Nutrition, South Dakota State University, Brookings, SD 57007, USA.
authors.forename: Haifa Abou
authors.initials: HA
authors.lastname: Samra
authors.forename: Bonny
authors.initials: B
authors.lastname: Specker
mesh_terms: D015502:Absorptiometry, Photon; D000367:Age Factors; D015519:Bone Density / Q000502:physiology*; D001846:Bone Development / Q000502:physiology*; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D016014:Linear Models; D008297:Male; D011336:Probability; D012737:Sex Factors; D047929:Term Birth; D016138:Walking / Q000502:physiology / Q000639:trends*