Advertisement

Dual pitch screw design provides equivalent fixation to upsized screw diameter in revision pedicle screw instrumentation: a cadaveric biomechanical study

      Abstract

      Background Context

      There are situations that require the replacement of pedicle screws. They are often exchanged when loose or broken or to accommodate a different sized rod or pedicle screw system. Traditionally, pedicle screws are replaced by up-sizing the core diameter until an interference fit is obtained. However, this method carries a risk of pedicle screw breach.

      Purpose

      To determine if dual pitch screws, with cancellous pitch in the vertebral body and cortical pitch throughout the pedicle, allows for in-line screw revision without upsizing screw diameter.

      Study Design

      Cadaveric biomechanical Study

      Patient Sample

      Not applicable

      Outcome Measures

      Not applicable

      Methods

      Pedicle screws were tested in the lumbar vertebrae from eleven cadavers. Standard pitch 5.5 mm screws were inserted and loaded using a "break-in" protocol. Screws were removed and replaced with one of four screw types: 5.5 mm Standard Pitch, 5.5 mm Dual Pitch, 6.0 mm Standard Pitch, or 6.0 mm Dual Pitch. Failure testing was done using a stepwise increasing cyclic loading protocol for 100 cycles at each increasing load level. The loading consisted of a combined axial and bending load simulating the load seen by the most inferior screw.

      Results

      Failure was consistent, with the tip of the screw displacing inferiorly into the vertebral body while simultaneously pulling out. Failure strength was lowest in the 5.5mm Standard (135.8±29.4N) followed by 6.0mm Standard (141.8±38.6N), 5.5mm Dual (158.1±53.8N), and 6.0mm Dual (173.6±52.1N, p=.023). There was no difference in the failure strength between the 5.5mm Dual and 6.0mm Standard. Lumbar level (p=.701) and donor spine (p=.062) were not associated with failure strength.

      Conclusions

      After pedicle screw removal, screws with a larger core diameter or with a dual pitch have similar failure strengths. Dual pitch screws may allow for in-line revision of screws without upsizing screw diameter, minimizing the risk of pedicle breach or fracture.

      Clinical Significance

      Dual pitch screws, with cancellous pitch in the vertebral body and cortical pitch through the pedicle, allows for in-line revision of pedicle screws without upsizing screw diameter; reducing the risk of pedicle breach or fracture when exchanging screws.

      Keywords

      To read this article in full you will need to make a payment

      Purchase one-time access:

      Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online access
      One-time access price info
      • For academic or personal research use, select 'Academic and Personal'
      • For corporate R&D use, select 'Corporate R&D Professionals'

      Subscribe:

      Subscribe to The Spine Journal
      Already a print subscriber? Claim online access
      Already an online subscriber? Sign in
      Institutional Access: Sign in to ScienceDirect

      References

        • Fujibayashi S
        • Takemoto M
        • Neo M
        • Matsuda S
        Strategy for salvage pedicle screw placement: A technical note.
        Int J Spine Surg. 2013; 7: e67-e71
        • Cook S
        • Barbera J
        • Rubi M
        • Salkeld S
        • Whitecloud T
        Lumbosacral fixation using expandable pedicle screws: an alternative in reoperation and osteoporosis.
        Spine J. 2001; 1: 109-114
        • Albanese K
        • Ordway NR
        • Albanese SA
        • Lavelle WF
        Effect of pedicle fill on axial pullout strength in spinal fixation after rod reduction.
        Orthopedics. 2017; 40: e990-e995
        • Mehta H
        • Santos E
        • Ledonio C
        • Sembran J
        • Ellingson A
        • Pare p
        • et al.
        Biomechanical analysis of pedicle screw pitch differential design in an osteoporotic cadaver model.
        Clin Biomech. 2012; 27: 234-240
        • Law M
        • Tencer AF
        • Anderson PA
        Caudo-cephalad loading of pedicle screws: mechanisms of loosening and methods of augmentation.
        Spine. 1993; 18: 2438-2443
        • Tan JS
        • Kwon BK
        • Dvorak MF
        • Fisher CG
        • Oxland TR
        Pedicle screw motion in the osteoporotic spine after augmentation with laminar hooks, sublaminar wires, or calcium phosphate cement: a comparative analysis.
        Spine. 2004; 29: 1723-1730
        • Carlson GD
        • Abitbol JJ
        • Anderson DR
        • Krag MH
        • Kostuik jp
        • Woo SL
        • et al.
        Screw fixation in the human sacrum: an in vitro study of the biomechanics of fixation.
        Spine. 1992; 17: S196-S203
        • Daftari TK
        • Horton WC
        • Hutton WC
        Correlations between screw hole preparation, torque of insertion, and pullout strength for spinal screws.
        J Spinal Disord. 1994; 2: 139-145
        • Okuyama K
        • Sato K
        • Abe E
        • Inaba H
        • Shimada Y
        • Murai H
        Stability of transpedicle screwing for the osteoporotic spine: An in vitro study of the mechanical stability.
        Spine. 1993; 18: 2240-2245
        • Polly D
        • Orchowski J
        • Ellenbogen R
        Revision pedicle screws: bigger, longer shims – what is best?.
        Spine. 1998; 12: 1374-1375
        • Ryken TC
        • Clausen JD
        • Traynelic VC
        • Goel VK
        Biomechanical analysis of bone mineral density, insertion technique, screw torque, and holding strength of anterior cervical plate screw.
        J Neurosurg. 1995; 83: 324-329
        • Snyder BD
        • Zaltz I
        • Hall JE
        • Emans JB
        Predicting the integrity of vertebral bone screw fixation in anterior spinal instrumentation.
        Spine. 1995; 20: 1568-1574
        • Zdeblick TA
        • Kunz DN
        • Cooke ME
        • McCabe R
        Pedicle screw pullout strength: correlation with insertional torque.
        Spine. 1993; 18: 1673-1676
        • Varghese V
        • Krishnan V
        • Kumar G
        Comparison of pullout strength of pedicle screws following revision using larger diameter screws.
        Med Eng Phys. 2019; 74: 180-185
        • Brasiliense LB
        • Lazaro BC
        • Reyes PM
        • Newcomb AG
        • Turner JL
        • Crandall DG
        • et al.
        Characteristics of immediate and fatigue strength of a mixed-pitched pedicle screw in cadaveric spine.
        Spine J. 2013; 13: 947-956
        • Seng W
        • Chou S
        • Siddiqui S
        • Oh J.
        Pedicle screw designs in spinal surgery: is there a difference? a biomechanical study on primary and revision pull-out strength.
        Spine. 2018; 44: e144-e149