title: The distribution of bone mass in the lumbar vertebrae: are we measuring the right target?
abstract: BACKGROUND
  The ideal target of bone mineral density (BMD) measurements of the spine is the trabecula-rich vertebral body. Yet, spine BMD measurements routinely obtained with dual-energy X-ray absorptiometry also include the posterior elements of the vertebra, which are mainly cortical bone and insensitive to bone loss.
  
  
  OBJECTIVE
  We compared the bone mass of the vertebral body and posterior elements to determine the contributions of vertebral components to vertebral BMD measurements.
  
  
  METHODS
  A micro-computed tomography study of lumbar vertebral bone.
  
  
  METHODS
  From a spine archive, 144 cadaveric lumbar vertebrae (L1-L5) from 48 male human spines (mean age, 50 years) were scanned in air using micro-computed tomography to measure bone volume, bone mineral content (BMC) and BMD of the vertebral body, posterior elements, and entire vertebra. The contributions of the vertebral components to the total vertebral BMC and volume were compared, and the correlations between the BMC and BMD of the vertebrae and their components were examined.
  
  
  RESULTS
  Overall, the vertebral body contributed about one-third of the total vertebral BMC and two-thirds of the total vertebral volume, and the posterior elements contributed the remainder. The vertebral body BMC and BMD were poorly correlated to those of the posterior elements (r=0.39 for BMC and r=0.34 for BMD, p<.0001) and moderately correlated to the whole vertebra (r=0.77 and 0.75, respectively, p<.0001). The BMC and BMD of the posterior elements and whole vertebra were more strongly correlated (r=0.89 and 0.84, respectively, p<.0001).
  
  
  CONCLUSIONS
  The posterior elements are the primary contributor to vertebral BMC and BMD measurements. Dual-energy X-ray absorptiometry spine BMD measurements are likely to be more representative of the posterior elements than the targeted vertebral body. The findings elucidate the extent of the limitation of dual-energy X-ray absorptiometry spine BMD measurements.
authors.affiliation: Spine Laboratory, Department of Orthopedic Surgery, The First Affiliated Hospital of Zhejiang University, 79#, Qingchun Road, Hangzhou, China, 310003; Faculty of Rehabilitation Medicine, University of Alberta, 3-44, 8205 114 St, Edmonton, Alberta, Canada T6G 2G4.
authors.forename: Yue
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Faculty of Rehabilitation Medicine, University of Alberta, 3-44, 8205 114 St, Edmonton, Alberta, Canada T6G 2G4.
authors.forename: Tapio
authors.initials: T
authors.lastname: Videman
authors.affiliation: Schulich School of Engineering, University of Calgary, 3280 Hospital Drive NW, Calgary, Alberta, Canada T2N 4Z6.
authors.forename: Steven K
authors.initials: SK
authors.lastname: Boyd
authors.affiliation: Faculty of Rehabilitation Medicine, University of Alberta, 3-44, 8205 114 St, Edmonton, Alberta, Canada T6G 2G4. Electronic address: mc.battie@ualberta.ca.
authors.forename: Michele C
authors.initials: MC
authors.lastname: Battié
mesh_terms: D015519:Bone Density; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D055114:X-Ray Microtomography
keywords: Bone mineral density; DXA; Lumbar spine; Osteoporosis; Vertebra; μCT