title: Calcium Triglyceride Versus Polymethylmethacrylate Augmentation: A Biomechanical Analysis of Pullout Strength.
abstract: METHODS
  Biomechanical pullout study using calcium triglyceride (CTG) and polymethylmethacrylate (PMMA) for screw augmentation.
  
  
  OBJECTIVE
  Compare the biomechanical performance of CTG augmentation versus the gold standard, PMMA, in primary and revision models, using a pedicle screw pullout model.
  CTG is a novel form of bone augmentation with several reported biocompatible properties compared with PMMA. PMMA is the standard of care for pedicle screw augmentation in osteoporotic spine.
  
  
  METHODS
  Blocks of closed-cell rigid polyurethane foam of uniform density, representing subcortical layer in osteoporotic pedicle, were prepared according to ASTM standards. After the components of PMMA (n = 11) and CTG (n = 11) were individually mixed in a standardized fashion, 0.2 ml was injected from deep to superficial along a predrilled pilot hole followed by immediate insertion of the pedicle screw. An unaugmented group (n = 10) was also prepared. Blocks cured for 24 hrs, and screws were pulled out at a rate of 5 mm/min on materials testing equipment. For the revision model, the unaugmented group, after screw pullout, was augmented with 0.8 ml of PMMA (n = 5) or CTG (n = 5) as detailed above and screw pullout performed similarly.
  
  
  RESULTS
  The mean pullout strengths (SD) for the intact models were as follows: unaugmented, 976.6 N (94.2 N); PMMA, 1,218.1 N (66.8 N); and CTG, 1,841.6 N (57.4 N). A one-way analysis of variance indicated a significant difference among the primary models (p < .0001). For the revision models, the pullout strength for PMMA was 1,939.2 N (108.9 N) and for CTG, 2,513.0 N (149.1 N), which were statistically different from each other (p < .0003). Stiffness of the constructs was increased with both PMMA and CTG augmentation over no augmentation (p < .0001) although no significant difference in stiffness was detected between the 2 forms of augmentation.
  
  
  CONCLUSIONS
  We conclude that CTG augmentation of pedicle screws resulted in significantly higher axial pullout strength in primary (p < .0001) and revision (p < .0003) models compared with PMMA.
authors.affiliation: Orthopaedic Research Laboratory, Departments of Orthopaedic Surgery and of Biomedical Engineering, Virginia Commonwealth University, McGuire Annex, 1112 East Clay St., Richmond, VA 23298, USA.
authors.forename: Lindsay E
authors.initials: LE
authors.lastname: Hickerson
authors.affiliation: Orthopaedic Research Laboratory, Departments of Orthopaedic Surgery and of Biomedical Engineering, Virginia Commonwealth University, McGuire Annex, 1112 East Clay St., Richmond, VA 23298, USA.
authors.forename: John R
authors.initials: JR
authors.lastname: Owen
authors.affiliation: Orthopaedic Research Laboratory, Departments of Orthopaedic Surgery and of Biomedical Engineering, Virginia Commonwealth University, McGuire Annex, 1112 East Clay St., Richmond, VA 23298, USA. Electronic address: jwayne@vcu.edu.
authors.forename: Jennifer S
authors.initials: JS
authors.lastname: Wayne
authors.affiliation: Tuckahoe Orthopaedic Associates, Ltd., 1501 Maple Ave., Suite 200, Richmond, VA 23226, USA.
authors.forename: H Robert
authors.initials: HR
authors.lastname: Tuten
keywords: Augmentation; Calcium triglyceride; Pedicle screw; Pullout