title: Does the cement stiffness affect fatigue fracture strength of vertebrae after cement augmentation in osteoporotic patients?
abstract: OBJECTIVE
  Normal progression of osteoporosis or the rigid reinforcement of the fractured vertebral body with polymethyl methacrylate (PMMA) cement is being discussed as a cause for adjacent-level fractures after vertebroplasty. The purpose of this study was to investigate whether augmentation with low stiffness cement can decrease the risk of adjacent-level fractures in low-quality bone.
  
  
  METHODS
  Eighteen female osteoporotic lumbar specimens (L1-L5) were harvested and divided into three groups according to bone mineral density: (I) native; (II) PMMA; (III) modified PMMA (lower stiffness). For the PMMA and modified PMMA groups, a compression fracture was first mechanically induced in L3, and then the fracture received vertebroplasty treatment. The cement stiffness reduction of the modified PMMA group was achieved via an addition of 8 mL of serum to the typical PMMA base. All specimens were exposed to cyclic loading (4 Hz) and a stepwise increasing applied peak force. Cement stiffness was tested according to ISO 5833.
  
  
  RESULTS
  A 51% decrease in cement stiffness was achieved in the modified PMMA group (954 ± 141 vs. 1,937 ± 478 MPa, p < 0.001). Fatigue fracture force (the force level during cyclic loading at which the deformation experienced a sudden increase; FFF) was significantly affected by bone quality (r (2) = 0.39, p = 0.006) and by the initial fracture force (the force necessary to create the initial fracture in L3 prior to augmentation; r (2) = 0.82, p < 0.001). Using initial fracture force as a covariate, the FFF of the modified PMMA group (1,764 ± 49 N) was significantly higher than in the PMMA group (1,544 ± 55 N; p = 0.03).
  
  
  CONCLUSIONS
  A possible method to reduce adjacent-level fractures after vertebroplasty in patients with reduced bone quality could be the use of a lower modulus cement. Therefore, mixing cement with biocompatible fluids could prove useful to tailor cement properties in the operating theater.
authors.affiliation: Department of Trauma-, Hand- and Reconstructive Surgery, University Medical Center Hamburg-Eppendorf, Martinistraße 52, 20246 Hamburg, Germany. j.kolb@uke.de
authors.forename: Jan Philipp
authors.initials: JP
authors.lastname: Kolb
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Kueny
authors.forename: Klaus
authors.initials: K
authors.lastname: Püschel
authors.forename: Andreas
authors.initials: A
authors.lastname: Boger
authors.forename: Johannes M
authors.initials: JM
authors.lastname: Rueger
authors.forename: Michael M
authors.initials: MM
authors.lastname: Morlock
authors.forename: Gerd
authors.initials: G
authors.lastname: Huber
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lehmann
mesh_terms: D001696:Biomechanical Phenomena; D001843:Bone Cements; D002102:Cadaver; D005260:Female; D006244:Hardness; D006801:Humans; D008422:Materials Testing; D058866:Osteoporotic Fractures / Q000601:surgery*; D016103:Spinal Fractures / Q000601:surgery*
chemical_list: D001843:Bone Cements