title: The functional muscle-bone unit in obese children - altered bone structure leads to normal strength strain index.
abstract: Obese children have a twofold increased risk of fracture of the forearm compared to non-obese children.
  
  
  OBJECTIVE
  To investigate bone strength and bone structure of the forearm, and the relationship between muscle and bone in obese children.
  
  
  METHODS
  The study-group consisted of 84 (40 female) overweight children (mean (SD)) age 11.8 (3.2) years, BMI 29.0 (5.1) kg/m(2)). Bone geometry and strength were measured at the proximal radius of the non-dominant forearm (65% measurement site) by means of pQCT (XCT 2000). Bone mineral density and lean mass of the total body was determined by means of DXA (Lunar, DPXL/PED). Results were compared to reference values by calculating age (SDS(CA)) and height-age (SDS(HA)) dependent standard deviation scores (SDS).
  
  
  RESULTS
  Cortical density, -1.11 (1.74) SDS(HA), -0.45 (1.52) SDS(CA); cortical thickness, -1.46 (1.33) SDS(HA), -1.01 (1.46) SDS(CA); cortical area, -0.42 (1.31) SDS(HA), 0.26 (1.58) SDS(CA); total bone area +2.21 (1.47) SDS(HA), 2.91 (1.80) SDS(CA), marrow area +3.12 (2.29) SDS(HA), 3.37 (2.38) SDS(CA); strength strain index +0.10 (1.10) SDS(HA), 0.95 (1.57) SDS(CA). These changes in bone structure were independent from pubertal stage. Measurements revealed correlations between muscle area and SSI (R(2)=0.67, p<0.001), and muscle mass and bone mineral content (DXA; R (2)=0.81, p<0.001).
  
  
  CONCLUSIONS
  Low cortical density, normal cortical area and increased total bone area led to a normal strength strain index adjusted both for height and for age. We assume that this normal bone strength is not appropriate for the higher kinetic energy of impact in case of a fall in overweight children.
authors.affiliation: Pediatric Endocrinology and Diabetology, University Children's Hospital, Tuebingen, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Ehehalt
authors.forename: G
authors.initials: G
authors.lastname: Binder
authors.forename: N
authors.initials: N
authors.lastname: Schurr
authors.forename: C
authors.initials: C
authors.lastname: Pfaff
authors.forename: M B
authors.initials: MB
authors.lastname: Ranke
authors.forename: R
authors.initials: R
authors.lastname: Schweizer
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D001848:Bone Diseases, Developmental / Q000503:physiopathology*; D001842:Bone and Bones / Q000293:injuries / Q000502:physiology*; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D008954:Models, Biological; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D009141:Musculoskeletal System / Q000503:physiopathology*; D009765:Obesity / Q000453:epidemiology / Q000503:physiopathology*; D013180:Sprains and Strains / Q000503:physiopathology; D055815:Young Adult