title: Porosity and Thickness of the Vertebral Endplate Depend on Local Mechanical Loading.
abstract: METHODS
  Mechanical and microcomputed tomography (micro-CT) study of cadaver spines.
  
  
  OBJECTIVE
  To compare porosity and thickness of vertebral endplates with (1) compressive stresses measured in adjacent intervertebral discs and (2) grade of disc degeneration.
  
  
  BACKGROUND
  Endplate porosity is important for disc metabolite transport, and yet porosity increases with age and disc degeneration. We hypothesize that porosity is largely determined by mechanical loading from adjacent discs.
  
  
  METHODS
  Forty motion segments (T8-9 to L4-5) were dissected from 23 cadavers aged 48 to 98 years. Each was subjected to 1 kN compression during which time intradiscal stresses were measured by pulling a pressure transducer along the disc's midsagittal diameter. "Stress profiles" revealed the average pressure in the nucleus, and the maximum stress in the anterior and posterior annulus. Specimens were further dissected to obtain discs with endplates (and 5 mm of bone) on either side. Microcomputed tomography scans (resolution 35 μm) were analyzed to calculate thickness and porosity in the midsagittal regions of all 80 endplates. Average values for the anterior, central, and posterior regions of each endplate were obtained. Disc degeneration was assessed macroscopically and microscopically.
  
  
  RESULTS
  Endplate porosity was inversely related to its thickness, being greatest in the central region opposite the nucleus, and least near the periphery. Superior endplates (relative to the disc) were 14% thicker (P < 0.001) and 4% less porous (P = 0.008) than inferior. In each of the 3 endplate regions (anterior, central, and posterior), porosity was inversely and significantly related to mechanical loading (pressure or maximum stress) in the adjacent disc region (P < 0.01 in all cases). Disc degeneration was best predicted by (reduced) nucleus pressure (R = 0.46, P < 0.001) and (reduced) maximum stress in the anterior annulus (R = 0.31, P < 0.001).
  
  
  CONCLUSIONS
  Mechanical loading is a major determinant of endplate thickness and porosity. Disc degeneration is more closely related to reduced disc stresses than to endplate thickness or porosity.
  
  
  METHODS
  N/A.
authors.affiliation: *Centre for Comparative and Clinical Anatomy and †School of Archaeology and Anthropology, University of Bristol, Bristol, United Kingdom.
authors.forename: Uruj
authors.initials: U
authors.lastname: Zehra
authors.forename: Kate
authors.initials: K
authors.lastname: Robson-Brown
authors.forename: Michael A
authors.initials: MA
authors.lastname: Adams
authors.forename: Patricia
authors.initials: P
authors.lastname: Dolan
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002102:Cadaver; D005260:Female; D006801:Humans; D007403:Intervertebral Disc; D055959:Intervertebral Disc Degeneration / Q000473:pathology*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D016062:Porosity; D013314:Stress, Mechanical; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging*; D016474:Weight-Bearing; D055114:X-Ray Microtomography