title: Augmentation of anterior vertebral body screw fixation by an injectable, biodegradable calcium phosphate bone substitute.
abstract: METHODS
  A biomechanical study to evaluate the effects of a biodegradable calcium phosphate (Ca-P) bone substitute on the fixation strength and bending rigidity of vertebral body screws.
  
  
  OBJECTIVE
  To determine if an injectable, biodegradable Ca-P bone substitute provides significant augmentation of anterior vertebral screw fixation in the osteoporotic spine.
  
  
  BACKGROUND
  Polymethylmethacrylate (PMMA) augmented screws have been used clinically; however, there is concern about thermal damage to the neural elements during polymerization of the PMMA as well as its negative effects on bone remodeling. Injectable, biodegradable Ca-P bone substitutes have shown enhanced fixation of pedicle screws.
  
  
  METHODS
  Sixteen fresh cadaveric thoracolumbar vertebrae were randomly divided into two groups: control (no augmentation) (n = 8) and Ca-P bone substitute augmentation (n = 8) groups. Bone-screw fixation rigidity in bending was determined initially and after 10(5) cycles, followed by pullout testing of the screw to failure to determine pullout strength and stiffness.
  
  
  RESULTS
  The bone-screw bending rigidity for the Ca-P bone substitute group was significantly greater than the control group, initially (58%) and after cyclic loading (125%). The pullout strength for Ca-P bone substitute group (1848 +/- 166 N) was significantly greater than the control group (665 +/- 92 N) (P < 0.01). Stiffness in pullout for the Ca-P bone substitute groups (399 +/- 69 N/mm) was significantly higher than the control group (210 +/- 51 N/mm) (P < 0.01).
  
  
  CONCLUSIONS
  This study demonstrated that augmentation of anterior vertebral body screw fixation with a biodegradable Ca-P bone substitute is a potential alternative to the use of PMMA cement.
authors.affiliation: Musculoskeletal Research Center, Department of Orthopaedic Surgery, Hospital for Joint Diseases Orthopaedic Institute, New New York, New York 10003, USA.
authors.forename: B
authors.initials: B
authors.lastname: Bai
authors.forename: F J
authors.initials: FJ
authors.lastname: Kummer
authors.forename: J
authors.initials: J
authors.lastname: Spivak
mesh_terms: D020341:Absorbable Implants; D001672:Biocompatible Materials; D001696:Biomechanical Phenomena; D001863:Bone Screws; D018786:Bone Substitutes / Q000008:administration & dosage*; D002102:Cadaver; D002130:Calcium Phosphates / Q000008:administration & dosage*; D006801:Humans; D016014:Linear Models; D010024:Osteoporosis / Q000601:surgery; D013123:Spinal Fusion / Q000295:instrumentation*; D013314:Stress, Mechanical
chemical_list: D001672:Biocompatible Materials; D018786:Bone Substitutes; D002130:Calcium Phosphates