title: Longitudinal changes in femur bone mineral density after spinal cord injury: effects of slice placement and peel method.
abstract: CONCLUSIONS
  Surveillance of femur metaphysis bone mineral density (BMD) decline after spinal cord injury (SCI) may be subject to slice placement error of 2.5%. Adaptations to anti-osteoporosis measures should exceed this potential source of error. Image analysis parameters likewise affect BMD output and should be selected strategically in longitudinal studies.
  
  
  BACKGROUND
  Understanding the longitudinal changes in bone mineral density (BMD) after spinal cord injury (SCI) is important when assessing new interventions. We determined the longitudinal effect of SCI on BMD of the femur metaphysis. To facilitate interpretation of longitudinal outcomes, we (1) determined the BMD difference associated with erroneous peripheral quantitative computed tomography (pQCT) slice placement, and (2) determined the effect of operator-selected pQCT peel algorithms on BMD.
  
  
  METHODS
  pQCT images were obtained from the femur metaphysis (12% of length from distal end) of adult subjects with and without SCI. Slice placement errors were simulated at 3 mm intervals and were processed in two ways (threshold-based vs. concentric peel).
  
  
  RESULTS
  BMD demonstrated a rapid decline over 2 years post-injury. BMD differences attributable to operator-selected peel methods were large (17.3% for subjects with SCI).
  
  
  CONCLUSIONS
  Femur metaphysis BMD declines after SCI in a manner similar to other anatomic sites. Concentric (percentage-based) peel methods may be most appropriate when special sensitivity is required to detect BMD adaptations. Threshold-based methods may be more appropriate when asymmetric adaptations are observed.
authors.affiliation: Graduate Program in Physical Therapy and Rehabilitation Science, The University of Iowa, 1-252 Medical Education Building, Iowa City, IA 52242-1190, USA.
authors.forename: S
authors.initials: S
authors.lastname: Dudley-Javoroski
authors.forename: R K
authors.initials: RK
authors.lastname: Shields
mesh_terms: D000293:Adolescent; D000328:Adult; D015519:Bone Density / Q000502:physiology*; D001851:Bone Diseases, Metabolic / Q000000981:diagnostic imaging / Q000209:etiology / Q000503:physiopathology; D003430:Cross-Sectional Studies; D018450:Disease Progression; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D013119:Spinal Cord Injuries / Q000150:complications / Q000503:physiopathology*; D014057:Tomography, X-Ray Computed / Q000379:methods; D055815:Young Adult
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