title: Revision of the failed pedicle screw in osteoporotic lumbar spine: biomechanical comparison of kyphoplasty versus transpedicular polymethylmethacrylate augmentation.
abstract: OBJECTIVE
  In this study, we aimed to compare of kyphoplasty versus transpedicular polymethylmethacrylate (PMMA) augmentation biomechanically in the revision of the failed pedicle screw in osteoporotic lumbar spine.
  
  
  METHODS
  Bone mineral density (BMD) of lumbar vertebrae collected from four bovines were measured. Each vertebra was decalcified with hydrochloric acid solution to obtain osteoporotic specimens. Primary polyaxial pedicle screws were inserted into the pedicles and pulled out until they failed. The pullout strength results of all specimens were recorded. Revision pedicle screws were randomly inserted into the same pedicles by either pedicle hole PMMA augmented (group 1) or kyphoplasty (Xvoid™) PMMA augmented pedicle screws (group 2). The pullout strength results of all specimens were re-recorded.
  
  
  RESULTS
  The mean BMD significantly decreased from 1.686 ± 227.9 g/cm(2) to 1.432 ± 157.1 g/cm(2) following decalcification (p<0.001). In group 1, the mean pullout strength of primary screws significantly decreased from 3443 ± 1086 N/m(2) to 2088 ± 924 N/m(2) following pedicle screw augmentation (p=0.006). In group 2, the mean pullout strength of primary screws decreased from 3702 ± 1063 N/m(2) to 3664 ± 1057 N/m(2) following kyphoplasty augmentation (p=0.934). Pedicle screw augmentation group achieved significantly lower pullout strength values than kyphoplasty pedicle hole augmentation group (p=0.002).
  
  
  CONCLUSIONS
  Although pedicle hole PMMA augmentation is the gold standard for the failed screws in an osteoporotic bone, kyphoplasty augmented pedicle screw seems to be more effective method increasing the pullout strength.
authors: Department of Orthopedics and Traumatology, Medical Faculty of Başkent University, Adana, Turkey.
authors: Alihan
authors: A
authors: Derinçek
authors: Mehmet
authors: M
authors: Türker
authors: Murat
authors: M
authors: Cinar
authors: Ozgür
authors: O
authors: Cetik
authors: Bariş
authors: B
authors: Kalaycioğlu
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001843:Bone Cements; D002417:Cattle; D004868:Equipment Failure; D005260:Female; D007738:Kyphosis / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000601:surgery; D058866:Osteoporotic Fractures / Q000601:surgery*; D065289:Pedicle Screws; D019904:Polymethyl Methacrylate / Q000008:administration & dosage; D012086:Reoperation
chemical_list: D001843:Bone Cements; D019904:Polymethyl Methacrylate