title: The effect of standard and low-modulus cement augmentation on the stiffness, strength, and endplate pressure distribution in vertebroplasty.
abstract: OBJECTIVE
  Vertebroplasty restores stiffness and strength of fractured vertebral bodies, but alters their stress transfer. This unwanted effect may be reduced by using more compliant cements. However, systematic experimental comparison of structural properties between standard and low-modulus augmentation needs to be done. This study investigated how standard and low-modulus cement augmentation affects apparent stiffness, strength, and endplate pressure distribution of vertebral body sections.
  
  
  METHODS
  Thirty-nine human thoracolumbar vertebral body sections were prepared by removing cortical endplates and posterior elements. The specimens were scanned with a HR-pQCT system and loaded in the elastic range. After augmentation with standard or low-modulus cement they were scanned again and tested in two steps. First, the contact pressure distribution between specimen and loading plates was measured with pressure-sensitive films. Then, they were loaded again in the elastic range and compressed until failure. Apparent stiffness was compared before and after augmentation, whereas apparent strength of augmented specimens was compared to a non-augmented reference group.
  
  
  RESULTS
  Vertebral body sections with fillings connecting both endplates were on average 33% stiffer and 47% stronger with standard cement, and 27% stiffer and 30% stronger with low-modulus cement. In contrast, partial fillings showed no significant strengthening for both cements and only a slight stiffness increase (<16%). The averaged endplate pressure above/below the cement was on average 15% lower with low-modulus cement compared to standard cement.
  
  
  CONCLUSIONS
  Augmentation connecting both endplates significantly strengthened and stiffened vertebral body sections also with low-modulus cement. A trend of reduced pressure concentrations above/below the cement was observed with low-modulus cement.
authors.affiliation: Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, Gusshausstrasse 27-29, 1040 Vienna, Austria. kinzl@ilsb.tuwien.ac.at
authors.forename: Michael
authors.initials: M
authors.lastname: Kinzl
authors.forename: Lorin M
authors.initials: LM
authors.lastname: Benneker
authors.forename: Andreas
authors.initials: A
authors.lastname: Boger
authors.forename: Philippe K
authors.initials: PK
authors.lastname: Zysset
authors.forename: Dieter H
authors.initials: DH
authors.lastname: Pahr
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001843:Bone Cements / Q000494:pharmacology*; D002102:Cadaver; D019245:Compressive Strength / Q000187:drug effects*; D004548:Elasticity / Q000187:drug effects*; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000293:injuries / Q000601:surgery; D008297:Male; D008875:Middle Aged; D019904:Polymethyl Methacrylate / Q000494:pharmacology; D012189:Retrospective Studies; D016103:Spinal Fractures / Q000601:surgery*; D013131:Spine / Q000187:drug effects* / Q000601:surgery; D013314:Stress, Mechanical; D013904:Thoracic Vertebrae / Q000293:injuries / Q000601:surgery; D054854:Vertebroplasty / Q000379:methods*; D016474:Weight-Bearing
chemical_list: D001843:Bone Cements; D019904:Polymethyl Methacrylate