title: Shear strength of the human lumbar spine.
abstract: BACKGROUND
  Shear loading is recognised as a risk factor for lower back pain. Previous studies of shear loading have either not addressed the influence of age, bone mineral density, axial height loss due to creep or were performed on animal specimens.
  
  
  METHODS
  Intact human lumbar motion segments (L2-3) were tested in shear using a modified materials testing machine, while immersed in a Ringer bath at 37°C. Vertebrae were rigidly embedded in neutral posture (0° flexion) and subjected to a constant axial compression load of 500 N. Shear was applied to three groups: 'Young-No-Creep' (20-42 years), 'Young-Creep' (22-38 years, creep 1000 N for 1h) and 'Old-No-Creep' (44-64 years). Failure was induced by up to 15 mm of anterior shear displacement at a rate of 0.5mm/s. The trabecular and apophyseal joint bone mineral densities were evaluated from computed tomography images of the intact lumbar spines.
  
  
  RESULTS
  Peak shear force correlated positively with trabecular bone mineral density for specimens tested without axial creep. No significant differences were observed with respect to age. During shear overload specimens increased in height in the axial direction.
  
  
  CONCLUSIONS
  Trabecular bone mineral density can be used to predict the peak force of lumbar spine in shear in neutral posture.
authors.affiliation: Institute of Biomechanics, TUHH Hamburg University of Technology, Hamburg, Germany. d.m.skrzypiec@leeds.ac.uk
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Skrzypiec
authors.forename: Anke
authors.initials: A
authors.lastname: Klein
authors.forename: Nicholas E
authors.initials: NE
authors.lastname: Bishop
authors.forename: Felix
authors.initials: F
authors.lastname: Stahmer
authors.forename: Klaus
authors.initials: K
authors.lastname: Püschel
authors.forename: Helmut
authors.initials: H
authors.lastname: Seidel
authors.forename: Michael M
authors.initials: MM
authors.lastname: Morlock
authors.forename: Gerd
authors.initials: G
authors.lastname: Huber
mesh_terms: D000328:Adult; D015519:Bone Density / Q000502:physiology*; D002102:Cadaver; D019245:Compressive Strength / Q000502:physiology; D055119:Elastic Modulus; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D033081:Shear Strength / Q000502:physiology; D013314:Stress, Mechanical; D013718:Tensile Strength / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology*