Oral Presentation 30th Australian and New Zealand Bone and Mineral Society Annual Scientific Meeting 2020

Heterogeneity in Microstructural Deterioration Following Spinal Cord Injury Reflects Site-Specificity of Mechano-transduction (#13)

Ali Ghasem-Zadeh 1 , Mary Galea 2 , Andrew Nunn 2 , Maya Panisset 2 , Xiao-Fang Wang 1 , Sandra Iuliano 1 , Steven Boyd 3 , Mark Forwood 4 , Ego Seeman 1
  1. Departments of Endocrinology and Medicine , Austin Health, the University of Melbourne, Heidelberg, VIC, Australia
  2. Vicroian Spinal Cord Service, Austin Health, University of Melbourne, Melbourne, VIC, Australia
  3. McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, Calgary, AB, Canada
  4. School of Medical Science and Menzies Health Institute Queensland, Griffith University, Gold Coast, Queensland, Australia

Background     Modeling and remodeling adapt bone morphology to accommodate strains encountered during usual loading.  If strains exceed a threshold that increases the likelihood of fracture, bone formation increases bone volume reducing these strains.  If unloading reduces strains below a threshold inhibiting resorption, bone resorption decreases bone volume restoring strains but perhaps at the price of compromised microstructure.  We hypothesized that weight-bearing regions, usually adapted to greater strains, suffer more bone loss and structural deterioration following spinal cord injury than regions commonly adapted to low strains. 

Methods           We quantified distal tibial, fibula and radius volumetric bone mineral density (vBMD) using high-resolution peripheral quantitative computed tomography in 32 men, mean age 43.5 years (range 23.5-75.0), 12 with tetraplegia and 20 with paraplegia of 0.5 to 18.6 years duration, and 102 healthy age-matched male controls.  Differences in morphology relative to controls were expressed as standardized deviation (SD) scores (mean ± SD).  Standardized mean differences in vBMD between the regions were expressed as SDs (95% confidence intervals, CI). 

Results              Compared to controls, men with tetraplegia had deficits in total vBMD at the distal tibia (-1.72±1.38 SD) (p<0.001) and distal fibula (-0.68±0.69 SD) (p=0.041), not distal radius(-0.21±0.96 SD) (p=0.641), despite paralysis.  Deficits in men with paraplegia were (-2.14±1.50 SD) (p<0.001) at the distal tibia and (-0.68±0.69 SD) (p=0.041) at the distal fibula while distal radial total vBMD was (0.23±1.02) (p=0.371), not increased, despite upper limb mobility.  Comparing regions, in men with tetraplegia, distal tibial total vBMD was 1.04 SD (95%CI -2.01, -0.07) lower than the distal fibula (p=0.037) and 1.51 SD (95%CI -2.57, - 0.45) lower than the distal radius (p=0.007); the latter two sites did not differ from each other.  Results were similar in men with paraplegia, but distal fibula total vBMD was 1.06 SD (-1.77, -0.35) lower than the distal radius (p=0.004).

Conclusion       Microarchitectural deterioration following spinal cord injury is heterogeneous, partly because the strain thresholds regulating the cellular activity of mechano-transduction are region specific.  

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