title: The Benefits of Cement Augmentation of Pedicle Screw Fixation Are Increased in Osteoporotic Bone: A Finite Element Analysis.
abstract: METHODS
  Biomechanical study using a finite element model of a normal and osteoporotic lumbar vertebrae comparing resistance with axial pullout and bending forces on polymethylmethacrylate-augmented and non-augmented pedicle screws.
  
  
  OBJECTIVE
  To compare the effect of cement augmentation of pedicle screw fixation in normal and osteoporotic bone with 2 different techniques of cement delivery.
  
  
  BACKGROUND
  Various clinical and biomechanical studies have addressed the benefits of cement augmentation of pedicle screws, but none have evaluated whether this effect is similar, magnified, or attenuated in osteoporotic bone compared with normal bone. In addition, no study has compared the biomechanical strength of augmented pedicle screws using cement delivery through the pedicle screw with delivery through a pilot hole.
  
  
  METHODS
  This study was funded by a grant from DePuy Synthes Spine. Normal and osteoporotic lumbar vertebrae with pedicle screws were simulated. The models were tested for screw pullout strength with and without cement augmentation. Two methods of cement delivery were also tested. Both methods were tested using 1 and 2.5 cm3volume of cement infiltrated in normal and osteoporotic bone.
  
  
  RESULTS
  The increase in screw pullout force was proportionally greater in osteoporotic bone with equivalent volumes of cement delivered. The researchers found that 1 and 2.5 cm3of cement infiltrated bone volume resulted in an increase in pullout force by about 50% and 120% in normal bone, and by about 64% and 156% in osteoporotic bone, respectively. The delivery method had only a minimal effect on pullout force when 2.5 cm3of cement was injected (<4% difference).
  
  
  CONCLUSIONS
  Cement augmentation increases the fixation strength of pedicle screws, and this effect is proportionately greater in osteoporotic bone. Cement delivery through fenestrated screws and delivery through a pilot hole result in comparable pullout strength at higher cement volumes.
authors.affiliation: Department of Mechanical Engineering, College of Engineering, Temple University, 1947 North 12th Street, Philadelphia, PA 19104, USA.
authors.forename: Wenhai
authors.initials: W
authors.lastname: Wang
authors.affiliation: Department of Mechanical Engineering, College of Engineering, Temple University, 1947 North 12th Street, Philadelphia, PA 19104, USA.
authors.forename: George R
authors.initials: GR
authors.lastname: Baran
authors.affiliation: Artemis Health Institute, Sector 51, Gurgaon 122001, Haryana, India.
authors.forename: Hitesh
authors.initials: H
authors.lastname: Garg
authors.affiliation: Shriners Hospitals for Children-Philadelphia, 3551 North Broad Street, Philadelphia, PA 19140, USA.
authors.forename: Randal R
authors.initials: RR
authors.lastname: Betz
authors.affiliation: DePuy Synthes Spine, Inc., 325 Paramount Drive, Raynham, MA 02767, USA.
authors.forename: Missoum
authors.initials: M
authors.lastname: Moumene
authors.affiliation: Shriners Hospitals for Children-Philadelphia, 3551 North Broad Street, Philadelphia, PA 19140, USA. Electronic address: pcahill@shrinenet.org.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Cahill
keywords: Cement; Finite element analysis; Osteoporosis; PMMA; Pedicle screw