title: The effect of pedicle expansion on pedicle morphology and biomechanical stability in the immature porcine spine.
abstract: METHODS
  Biomechanical study in an animal model.
  
  
  OBJECTIVE
  To evaluate the feasibility of sequential dilation of the immature pedicles by dilators and to determine the biomechanical stability of screws placed in these expanded pedicles.
  
  
  BACKGROUND
  Pedicle screws have become the implant of choice in spinal fixation. Secondary to the small vertebra sizes of pediatric patients and difficulty in finding appropriate screw sizes, they have found limited use in pediatric spine. Dilation of the pediatric pedicles may overcome the limitation secondary to discrepancy between screw sizes. However, there are no data in the literature regarding dilation capacity of pediatric pedicles to enable larger pedicle screw fixation.
  
  
  METHODS
  Two-month-old domestic pig vertebrae were used. The right pedicles were dilated with stainless steel dilators just before there is visual evidence of pedicle failure. The left pedicles served as a control group. The inner and outer diameters of the pedicles were measured on the CT scans before and after dilation. The pedicles were instrumented with 3.5-mm pedicle screws at the thoracic level and 4.0-mm pedicle screws at the lumbar level. The pullout strength of each pedicle was measured.
  
  
  RESULTS
  The dilation procedure resulted in an increase in both inner (2.59 +/- 0.75 to 3.32 +/- 0.58 mm) and outer diameters (5.43 +/- 0.95 to 6.21 +/- 0.96 mm) (P < 0.05). The inner diameters dilated more than the outer diameters (34.3% vs. 15.0%). The pullout strength of the expanded pedicles (320.1 +/- 83.9 N) was significantly lower than the nonexpanded ones (408.1 +/- 102.0 N) (P < 0.01).
  
  
  CONCLUSIONS
  This study demonstrated that immature pedicles can be expanded by application of serial dilators. However, dilation significantly decreases the pullout strength of the pedicle.
authors.affiliation: Hacettepe University, Faculty of Medicine, Department of Orthopedics, Sihhiye, Ankara, 06100, Turkey. yazioglu@hacettepe.edu.tr
authors.forename: Muharrem
authors.initials: M
authors.lastname: Yazici
authors.forename: Murat
authors.initials: M
authors.lastname: Pekmezci
authors.forename: Akin
authors.initials: A
authors.lastname: Cil
authors.forename: Ahmet
authors.initials: A
authors.lastname: Alanay
authors.forename: Emre
authors.initials: E
authors.lastname: Acaroglu
authors.forename: Fethullah C
authors.initials: FC
authors.lastname: Oner
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001696:Biomechanical Phenomena / Q000295:instrumentation*; D001863:Bone Screws; D011859:Radiography; D013131:Spine / Q000000981:diagnostic imaging / Q000502:physiology* / Q000601:surgery*; D034421:Sus scrofa