title: Biomechanical Performance of Various Cement-Augmented Cannulated Pedicle Screw Designs for Osteoporotic Bones.
abstract: BACKGROUND
  Early-stage pullout is a common problem for surgeons during the fixation of osteoporotic bones. Poor bone quality limits the use of pedicle screws for patients with osteoporosis. In this study, the researchers investigated the effects of hole and gap position and type on the pullout strength of cannulated screws.
  
  
  METHODS
  Seven different designs were tested, including a control group. All cannula diameters were 2 mm and holes were drilled with a diameter of 1.5 mm. Gaps were milled with a 2-mm-diameter tool with 2-mm displacement proximally. All holes and gaps were drilled or opened unilaterally and bilaterally. Grade 40 and 10 polyurethane foam was used to simulate healthy and osteoporotic bones, respectively. For pullout tests, insertion depth was 30 mm and 2-mm-diameter pilot holes were drilled into blocks before screws were inserted. The cross-head speed was 2 mm/min. For torsion tests, 1 side of the screw was fixed and other was twisted clockwise.
  
  
  RESULTS
  For torsion tests, the maximum torque value exhibited by the control group (non-cannulated) was 14.94 Nm. The highest torsional strength among tested cannulated screws was 13.54 Nm for Single side two holes including design (S2H) (p < .0001). The minimum torsional strength was 9.45 Nm with a breaking angle of 39° (p < .005). Comparing results for samples pulled out from grade 40 polyurethane foam, single side slot including design (SS) samples exhibited the highest pullout strength with a maximum force of 3,104 N.
  
  
  CONCLUSIONS
  The unilateral, sequential, 3-radial hole, drilled, cannulated screw was the optimal alternative when considering pullout and torsional strength as criteria.
authors.affiliation: Department of Orthopaedics, Yenimahalle Training and Research Hospital, 2026. Avenue, 06370, Ankara, Turkey.
authors.forename: Tolga
authors.initials: T
authors.lastname: Tolunay
authors.affiliation: Department of Orthopaedics, Yenimahalle Training and Research Hospital, 2026. Avenue, 06370, Ankara, Turkey.
authors.forename: Kağan
authors.initials: K
authors.lastname: Arslan
authors.affiliation: Department of Mechanical Engineering, TOBB University of Economics and Technology, Sogutozu Avenue, 06560, Ankara, Turkey.
authors.forename: Onur
authors.initials: O
authors.lastname: Yaman
authors.affiliation: Department of Neurosurgery, Neurospinal Academy, Istanbul, Turkey.
authors.forename: Sedat
authors.initials: S
authors.lastname: Dalbayrak
authors.affiliation: Department of Mechanical Engineering, TOBB University of Economics and Technology, Sogutozu Avenue, 06560, Ankara, Turkey. Electronic address: tdemir@etu.edu.tr.
authors.forename: Teyfik
authors.initials: T
authors.lastname: Demir
keywords: Cement augmentation; Pedicle screw design; Pullout