title: Bone mineral and stiffness loss at the distal femur and proximal tibia in acute spinal cord injury.
abstract: CONCLUSIONS
  Computed tomography and finite element modeling were used to assess bone mineral and stiffness loss at the knee following acute spinal cord injury (SCI). Marked bone mineral loss was observed from a combination of trabecular and endocortical resorption. Reductions in stiffness were 2-fold greater than reductions in integral bone mineral.
  
  
  BACKGROUND
  SCI is associated with a rapid loss of bone mineral and an increased rate of fragility fracture. The large majority of these fractures occur around regions of the knee. Our purpose was to quantify changes to bone mineral, geometry, strength indices, and stiffness at the distal femur and proximal tibia in acute SCI.
  
  
  METHODS
  Quantitative computed tomography (QCT) and patient-specific finite element analysis were performed on 13 subjects with acute SCI at serial time points separated by a mean of 3.5 months (range 2.6-4.8 months). Changes in bone mineral content (BMC) and volumetric bone mineral density (vBMD) were quantified for integral, trabecular, and cortical bone at epiphyseal, metaphyseal, and diaphyseal regions of the distal femur and proximal tibia. Changes in bone volumes, cross-sectional areas, strength indices and stiffness were also determined.
  
  
  RESULTS
  Bone mineral loss was similar in magnitude at the distal femur and proximal tibia. Reductions were most pronounced at epiphyseal regions, ranging from 3.0 % to 3.6 % per month for integral BMC (p < 0.001) and from 2.8 % to 3.4 % per month (p < 0.001) for integral vBMC. Trabecular BMC decreased by 3.1-4.4 %/month (p < 0.001) and trabecular vBMD by 2.7-4.7 %/month (p < 0.001). A 3.8-5.4 %/month reduction was observed for cortical BMC (p < 0.001); the reduction in cortical vBMD was noticeably lower (0.6-0.8 %/month; p ≤ 0.01). The cortical bone loss occurred primarily through endosteal resorption, and reductions in strength indices and stiffness were some 2-fold greater than reductions in integral bone mineral.
  
  
  CONCLUSIONS
  These findings highlight the need for therapeutic interventions targeting both trabecular and endocortical bone mineral preservation in acute SCI.
authors.affiliation: Department of Kinesiology and Nutrition, University of Illinois at Chicago, 1919 W. Taylor Street, 650 AHSB, M/C 517, Chicago, IL, 60621, USA, wbedward@ucalgary.ca.
authors.forename: W B
authors.initials: WB
authors.lastname: Edwards
authors.forename: T J
authors.initials: TJ
authors.lastname: Schnitzer
authors.forename: K L
authors.initials: KL
authors.lastname: Troy
mesh_terms: D015502:Absorptiometry, Photon; D000208:Acute Disease; D000328:Adult; D015519:Bone Density / Q000502:physiology; D019245:Compressive Strength / Q000502:physiology; D018483:Diaphyses / Q000503:physiopathology; D004838:Epiphyses / Q000503:physiopathology; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000503:physiopathology*; D005500:Follow-Up Studies; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D010024:Osteoporosis / Q000000981:diagnostic imaging / Q000209:etiology* / Q000503:physiopathology; D013119:Spinal Cord Injuries / Q000150:complications* / Q000503:physiopathology; D013977:Tibia / Q000000981:diagnostic imaging / Q000503:physiopathology*; D014057:Tomography, X-Ray Computed / Q000379:methods; D055815:Young Adult