title: Mechanical performance of cylindrical and dual-core pedicle screws after repeated insertion.
abstract: METHODS
  Ex vivo study of the mechanical performance of cylindrical and dual-core pedicle screws after insertion, removal, and reinsertion in the same hole.
  
  
  OBJECTIVE
  To evaluate the effect of repeated use of same screw hole on the insertion torque and the retentive strength of the cylindrical and dual-core screws.
  
  
  BACKGROUND
  Insertion and removal of pedicle screws is sometimes necessary during surgical procedure to assess the integrity of the pilot-hole wall. However, this maneuver may compromise the implant-holding capacity.
  
  
  METHODS
  Sixty thoracolombar vertebrae (T13–L5), harvested from 10 healthy calves, were used to insert 2 different designs of pedicle screws: cylindrical (5.0-mm outer diameter) and dual-core screws (5.2-mm outer diameter). Three experimental groups were created on the basis of the number of insertions of the screws and 2 subgroups were established according to the core pedicle screw design (dual-core and cylindrical). The insertion torque was measured during initial insertion, second insertion, and third insertion. Pullout screw tests were performed using a universal testing machine to evaluate the pullout strength after initial insertion, second insertion, and third insertion.
  
  
  RESULTS
  Significant reductions of 38% in mean insertion torque and 30% in mean pullout strength of dual-core screw were observed between the initial insertion and the third insertion. The cylindrical screw observed significant reductions of 52.5% in mean insertion torque and 42.3% in mean pullout strength between the initial insertion and the third insertion. A reduction of mean insertion torque and pullout strength between the first insertion and the second insertion but without significance was also observed for both types of screws.
  
  
  CONCLUSIONS
  Insertions and reinsertion of either cylindrical or dual-core pedicle screws have compromised insertion torque and pullout strength of the implants as measured by mechanical tests.
authors.affiliation: Department of Biomechanics, Medicine and Rehabilitation of the Locomotor Apparatus, Faculty of Medicine of Ribeirão Preto, USP, Brazil. hladefi n@fmrp.usp.br
authors.forename: Helton L A
authors.initials: HL
authors.lastname: Defino
authors.forename: Rodrigo César
authors.initials: RC
authors.lastname: Rosa
authors.forename: Patrícia
authors.initials: P
authors.lastname: Silva
authors.forename: Antonio Carlos
authors.initials: AC
authors.lastname: Shimano
authors.forename: Francisco José
authors.initials: FJ
authors.lastname: Albuquerque de Paula
authors.forename: José Batista
authors.initials: JB
authors.lastname: Volpon
mesh_terms: D000818:Animals; D001863:Bone Screws / Q000592:standards*; D002417:Cattle; D017743:Equipment Reuse; D008159:Lumbar Vertebrae / Q000601:surgery*; D008422:Materials Testing / Q000379:methods; D015203:Reproducibility of Results; D013123:Spinal Fusion / Q000295:instrumentation*; D013904:Thoracic Vertebrae / Q000601:surgery*; D019415:Torque