title: Which is the preferred revision technique for loosened iliac screw? A novel technique of boring cement injection from the outer cortical shell.
abstract: METHODS
  An in vitro biomechanical cadaver study.
  
  
  OBJECTIVE
  To evaluate the pull-out strength after 5000 cyclic loading among 4 revision techniques for the loosened iliac screw using corticocancellous bone, longer screw, traditional cement augmentation, and boring cement augmentation.
  
  
  BACKGROUND
  Iliac screw loosening is still a clinical problem for lumbo-iliac fusion. Although many revision techniques using corticocancellous bone, larger screw, and polymethylmethacrylate (PMMA) augmentation were applied in repairing pedicle screw loosening, their biomechanical effects on the loosened iliac screw remain undetermined.
  
  
  METHODS
  Eight fresh human cadaver pelvises with the bone mineral density values ranging from 0.83 to 0.97 g/cm were adopted in this study. After testing the primary screw of 7.5 mm diameter and 70 mm length, 4 revision techniques were sequentially established and tested on the same pelvis as follows: corticocancellous bone, longer screw with 100 mm length, traditional PMMA augmentation, and boring PMMA augmentation. The difference of the boring technique from traditional PMMA augmentation is that PMMA was injected into the screw tract through 3 boring holes of outer cortical shell without removing the screw. On an MTS machine, after 5000 cyclic compressive loading of -200∼-500 N to the screw head, axial maximum pull-out strengths of the 5 screws were measured and analyzed.
  
  
  RESULTS
  The pull-out strengths of the primary screw and 4 revised screws with corticocancellous bone, longer screw and traditional and boring PMMA augmentation were 1167 N, 361 N, 854 N, 1954 N, and 1820 N, respectively. Although longer screw method obtained significantly higher pull-out strength than corticocancellous bone (P<0.05), the revised screws using these 2 techniques exhibited notably lower pull-out strength than the primary screw and 2 PMMA-augmented screws (P<0.05). Either traditional or boring PMMA screw showed obviously higher pull-out strength than the primary screw (P<0.05); however, no significant difference of pull-out strength was detected between the 2 PMMA screws (P>0.05).
  
  
  CONCLUSIONS
  Wadding corticocancellous bone and increasing screw length failed to provide sufficient anchoring strength for a loosened iliac screw; however, both traditional and boring PMMA-augmented techniques could effectively increase the fixation strength. On the basis of the viewpoint of minimal invasion, the boring PMMA augmentation may serve as a suitable salvage technique for iliac screw loosening.
authors.affiliation: Department of Spine Surgery and Orthopaedic Research Institution, First Affiliated Hospital, 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: Zhan-Kun
authors.initials: ZK
authors.lastname: Yang
authors.forename: Ze-Min
authors.initials: ZM
authors.lastname: Li
authors.forename: Li-Wen
authors.initials: LW
authors.lastname: Zeng
authors.forename: Li-Bing
authors.initials: LB
authors.lastname: Wang
authors.forename: William Weijia
authors.initials: WW
authors.lastname: Lu
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001843:Bone Cements; D001863:Bone Screws; D005260:Female; D006801:Humans; D007085:Ilium / Q000601:surgery*; D016268:Internal Fixators; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011475:Prosthesis Failure; D012086:Reoperation
chemical_list: D001843:Bone Cements