title: Vertebral deformity arising from an accelerated "creep" mechanism.
abstract: BACKGROUND
  Vertebral deformities often occur in patients who recall no trauma, and display no evident fracture on radiographs. We hypothesise that vertebral deformity can occur by a gradual creep mechanism which is accelerated following minor damage. "Creep" is continuous deformation under constant load.
  
  
  METHODS
  Forty-five thoracolumbar spine motion segments were tested from cadavers aged 42-92 years. Vertebral body areal BMD was measured using DXA. Specimens were compressed at 1 kN for 30 min, while creep in each vertebral body was measured using an optical MacReflex system. After 30 min recovery, each specimen was subjected to a controlled overload event which caused minor damage to one of its vertebrae. The creep test was then repeated.
  
  
  RESULTS
  Vertebral body creep was measurable in specimens with BMD <0.5 g/cm(2). Creep was greater anteriorly than posteriorly (p < 0.001), so that vertebrae gradually developed a wedge deformity. Compressive overload reduced specimen height by 2.24 mm (STD 0.77 mm), and increased vertebral body creep by 800 % (anteriorly), 1,000 % (centrally) and 600 % (posteriorly). In 34 vertebrae with complete before-and-after data, anterior wedging occurring during the 1st creep test averaged 0.07° (STD 0.17°), and in the 2nd test (after minor damage) it averaged 0.79° (STD 1.03°). The increase was highly significant (P < 0.001). Vertebral body wedging during the 2nd creep test was proportional to the severity of damage, as quantified by specimen height loss during the overload event (r (2) = 0.51, p < 0.001, n = 34).
  
  
  CONCLUSIONS
  Minor damage to an old vertebral body, even if it is barely discernible on radiographs, can accelerate creep to such an extent that it makes a substantial contribution to vertebral deformity.
authors.affiliation: University of Roehampton, London, UK. Jin.Luo@roehampton.ac.uk
authors.forename: Jin
authors.initials: J
authors.lastname: Luo
authors.forename: Phillip
authors.initials: P
authors.lastname: Pollintine
authors.forename: Edward
authors.initials: E
authors.lastname: Gomm
authors.forename: Patricia
authors.initials: P
authors.lastname: Dolan
authors.forename: Michael A
authors.initials: MA
authors.lastname: Adams
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density; D002102:Cadaver; D006801:Humans; D008159:Lumbar Vertebrae / Q000293:injuries* / Q000473:pathology*; D008875:Middle Aged; D013904:Thoracic Vertebrae / Q000293:injuries* / Q000473:pathology*