title: Regional Variations in Shear Strength and Density of the Human Thoracic Vertebral Endplate and Trabecular Bone.
abstract: BACKGROUND
  Previous studies investigated the overall mechanical strength of the vertebral body; however, limited information is available on the biomechanical properties of different regions within the vertebral endplate and cancellous bone. In addition, the correlation between mechanical strength and various density measurements has not been studied yet.
  
  
  METHODS
  Thoracic (T10) vertebrae were harvested from fifteen human cadaveric spines (average age: 77 years old). Twelve cylindrical cores of 7.2 mm (diameter) by 3.2 mm (height) were prepared from each vertebral body. Shear was produced using a stainless steel tubular blade and measured with a load cell from a mechanical testing machine. Optical and bulk densities were calculated before mechanical testing. Apparent, material, and ash densities were measured after testing.
  
  
  RESULTS
  Material density and shear strength increased from anterior to lateral regions of both endplate and cancellous bone. Endplate shear strength was significantly lower in the anterior (0.52 ± 0.08 MPa) than in the lateral region (2.72 ± 0.59 MPa) (p=0.017). Trabecular bone maximum load carrying capacity was 5 times higher in the lateral (12 ± 2.74 N) (p=0.09) and 4.5 times higher in the central (10 ± 2.24 N) (p=0.2) than in the anterior (2 ± 0.60 N) regions. Mechanical strength positively correlated with ash density, and even moreso with material density.
  
  
  CONCLUSIONS
  Shear strength was the lowest at the anterior region and highest at the lateral region for both endplate and cancellous bone. Material density had the best correlation with mechanical strength. Newer spinal implants could optimize the loading in the lateral aspects of both endplate and cancellous bone to reduce the likelihood of screw loosening and the subsidence of disc replacement devices. This study was reviewed by the SUNY Downstate Medical Center IRB Committee; IRB#: 533603-2.
authors.affiliation: SUNY Downstate Medical Center, Brooklyn, New York, New York 11203.
authors.forename: Fred
authors.initials: F
authors.lastname: Xavier
authors.affiliation: SUNY Downstate Medical Center, Brooklyn, New York, New York 11203.
authors.forename: Julio J
authors.initials: JJ
authors.lastname: Jauregui
authors.affiliation: SUNY Downstate Medical Center, Brooklyn, New York, New York 11203.
authors.forename: Nathan
authors.initials: N
authors.lastname: Cornish
authors.affiliation: SUNY Downstate Medical Center, Brooklyn, New York, New York 11203.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Jason-Rousseau
authors.affiliation: SUNY Downstate Medical Center, Brooklyn, New York, New York 11203.
authors.forename: Dipal
authors.initials: D
authors.lastname: Chatterjee
authors.affiliation: SUNY Downstate Medical Center, Brooklyn, New York, New York 11203.
authors.forename: Gavriel
authors.initials: G
authors.lastname: Feuer
authors.affiliation: SUNY Downstate Medical Center, Brooklyn, New York, New York 11203.
authors.forename: Westley
authors.initials: W
authors.lastname: Hayes
authors.affiliation: SUNY Downstate Medical Center, Brooklyn, New York, New York 11203.
authors.forename: Bhaveen H
authors.initials: BH
authors.lastname: Kapadia
authors.affiliation: SUNY Downstate Medical Center, Brooklyn, New York, New York 11203.
authors.forename: John N
authors.initials: JN
authors.lastname: Carter
authors.affiliation: SUNY Downstate Medical Center, Brooklyn, New York, New York 11203.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Yoshihara
authors.affiliation: SUNY Downstate Medical Center, Brooklyn, New York, New York 11203.
authors.forename: Subrata
authors.initials: S
authors.lastname: Saha
keywords: bone density; cancellous bone; endplate; osteoporosis; shear strength; vertebral fracture