title: Bone density, structure, and strength in juvenile idiopathic arthritis: importance of disease severity and muscle deficits.
abstract: OBJECTIVE
  To identify determinants of musculoskeletal deficits (muscle cross-sectional area [mCSA], trabecular volumetric bone mineral density [vBMD], and cortical bone strength [section modulus]) in patients with juvenile idiopathic arthritis (JIA) and to determine if cortical bone strength is appropriately adapted to muscle forces.
  
  
  METHODS
  Peripheral quantitative computed tomography (pQCT) of the tibia was performed in 101 patients with JIA (79% female; 24 with oligoarticular JIA, 40 with polyarticular JIA, 18 with systemic JIA, and 19 with spondylarthritis [SpA]) and 830 healthy control subjects; all were ages 5-22 years. Outcomes of pQCT were expressed as sex- and race-specific Z scores. Multivariable linear regression models assessed mCSA and bone status in JIA patients compared with controls and identified factors associated with musculoskeletal deficits in JIA.
  
  
  RESULTS
  The median duration of JIA was 40 months; 29% of the JIA patients had active arthritis, and 28% had received glucocorticoid therapy during the previous year. Compared with the controls, the mCSA and section modulus Z scores were significantly lower in patients with polyarticular JIA and those with SpA. Trabecular vBMD Z scores were significantly lower in patients with polyarticular JIA, those with systemic JIA, and those with SpA. Significant predictors of musculoskeletal deficits included active arthritis in the previous 6 months (mCSA), temporomandibular joint disease (mCSA and section modulus), functional disability (mCSA and vBMD), short stature (vBMD), infliximab exposure (vBMD), and JIA duration (section modulus). The section modulus was significantly reduced relative to mCSA in patients with JIA after adjustment for age and limb length.
  
  
  CONCLUSIONS
  Marked deficits in vBMD and bone strength occur in JIA in association with severe and longstanding disease. Contrary to the findings of previous studies, bone deficits were greater than expected relative to the mCSA, which illustrates the importance of adjusting for age and bone length.
authors.affiliation: Children's Hospital of Philadelphia, and University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA. burnhams@email.chop.edu <burnhams@email.chop.edu>
authors.forename: Jon M
authors.initials: JM
authors.lastname: Burnham
authors.forename: Justine
authors.initials: J
authors.lastname: Shults
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Dubner
authors.forename: Harjeet
authors.initials: H
authors.lastname: Sembhi
authors.forename: Babette S
authors.initials: BS
authors.lastname: Zemel
authors.forename: Mary B
authors.initials: MB
authors.lastname: Leonard
mesh_terms: D000293:Adolescent; D000328:Adult; D001171:Arthritis, Juvenile / Q000188:drug therapy / Q000473:pathology* / Q000503:physiopathology*; D015519:Bone Density / Q000502:physiology*; D001842:Bone and Bones / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology*; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D005260:Female; D005938:Glucocorticoids / Q000627:therapeutic use; D006801:Humans; D016014:Linear Models; D008297:Male; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D012720:Severity of Illness Index; D014057:Tomography, X-Ray Computed
chemical_list: D005938:Glucocorticoids