title: Biomechanical effects of insertion location and bone cement augmentation on the anchoring strength of iliac screw.
abstract: BACKGROUND
  Iliac screw loosening has been a clinical problem in the lumbo-pelvic reconstruction. Although iliac screws are commonly inserted into either upper or lower iliac column, the biomechanical effects of the two fixations and their revision techniques with bone cement remain undetermined. The purpose of this study was to compare the anchoring strengths of the upper and lower iliac screws with and without cement augmentation.
  
  
  METHODS
  5 pairs of formalin fixed cadaveric ilia with the bone mineral density values ranged from 0.82 to 0.97 g/cm(2) were adopted in this study. Using screws with 70-mm length and 7.5-mm diameter, 2 conventional iliac screw fixations and their revision techniques with cement augmentation were sequentially established and tested on the same ilium as follows: upper screw, upper cement screw, lower screw, and lower cement screw. Following 2000 cyclic compressive loading of -300 N to -100 N to the screw on a material testing machine, the maximum pull-out strengths were measured and analyzed.
  
  
  RESULTS
  The average pull-out strengths of upper, upper cement, lower, and lower cement screws were 964 N, 1462 N, 1537 N, and 1964 N, respectively. The lower screw showed significantly higher pull-out strength than the upper one (P=0.008). The cement augmentation notably increased the pull-out strengths of both upper and lower screws. The positive correlation between pull-out strength and bone mineral density value was obtained for the 4 fixations.
  
  
  CONCLUSIONS
  The lower iliac screw technique should be the preferred choice in lumbo-pelvic stabilization surgery; cement augmentation may serve as a useful salvage technique for iliac screw loosening; preoperative evaluation of bone quality is crucial for predicting fixation strength of iliac screw.
authors.affiliation: Department of Spine Surgery, the First Affiliated Hospital and Orthopedic Research Institute of Sun Yat-sen University, 183 Huangpu East Road, Guangzhou, China. hpyubinsheng@hotmail.com
authors.forename: Bin-Sheng
authors.initials: BS
authors.lastname: Yu
authors.forename: Ze-Min
authors.initials: ZM
authors.lastname: Li
authors.forename: Zhi-Yu
authors.initials: ZY
authors.lastname: Zhou
authors.forename: Li-Wen
authors.initials: LW
authors.lastname: Zeng
authors.forename: Li-Bing
authors.initials: LB
authors.lastname: Wang
authors.forename: Zhao-Min
authors.initials: ZM
authors.lastname: Zheng
authors.forename: William Weijia
authors.initials: WW
authors.lastname: Lu
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001843:Bone Cements / Q000737:chemistry*; D015519:Bone Density; D001863:Bone Screws; D005260:Female; D006801:Humans; D007085:Ilium / Q000737:chemistry; D008297:Male; D008875:Middle Aged; D010384:Pelvic Bones / Q000473:pathology; D010388:Pelvis / Q000473:pathology; D013314:Stress, Mechanical
chemical_list: D001843:Bone Cements