European Spine Journal

, Volume 19, Issue 5, pp 803–808 | Cite as

Load sharing properties of cervical pedicle screw-rod constructs versus lateral mass screw-rod constructs

  • Bradley J. Dunlap
  • Eldin E. Karaikovic
  • Hyung-Soon Park
  • Mark J. Sokolowski
  • Li-Qun Zhang
Original Article

Abstract

Lateral mass screws have a history of successful clinical use, but cannot always be used in the subaxial cervical spine. Despite safety concerns, cervical pedicle screws have been proposed as an alternative. Pedicle screws have been shown to be biomechanically stronger than lateral mass screws. No study, however, has investigated the load sharing properties comparing constructs using these screws. To investigate this, 12 fresh-frozen single cervical spine motion segments (C4–5 and C6–7) from six cadavers were isolated. They were randomized to receive either lateral mass or pedicle screw-rod constructs. After preloading, the segments were cyclically loaded with a uniplanar axial load from 0 to 90 N both with and without the construct in place. Pressure data at the disc space were continuously collected using a dynamic pressure sensor. The reduction in disc space pressure between the two constructs was calculated to see if pedicle screw and lateral mass screw-rod constructs differed in their load sharing properties. In both the pedicle screw and lateral mass screw-rod constructs, there was a significant reduction in the disc space pressures from the no-construct to construct conditions. The percentage decrease for the pedicle screw constructs was significantly greater than the percentage decrease for the lateral mass screw constructs for average pressure (p ≤ 0.002), peak pressure (p ≤ 0.03) and force (p ≤ 0.04). We conclude that cervical pedicle screw-rod constructs demonstrated a greater reduction in axial load transfer through the intervertebral disc than lateral mass screw-rod constructs. Though there are dangers associated with the insertion of cervical pedicle screws, their use might be advantageous in some clinical conditions when increased load sharing is necessary.

Keywords

Cervical spine Biomechanics Cervical pedicle screws Lateral mass screws 

Notes

Acknowledgments

The authors would like to thank the following: Eugene P. Lautenschlager, PhD, Northwestern University Department of Orthopaedic Surgery, for his assistance with the statistical analysis; Usha Periyanayagam, third year medical student, Northwestern University Feinberg School of Medicine, for her assistance with radiographic examination of the specimens; Northwestern Center for Advanced Surgical Education for their assistance with procuring some of the specimens; Depuy Spine for donating the screws and instrumentation used in this experiment.

Conflict of interest statement

Depuy Spine provided implants used in the study.

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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • Bradley J. Dunlap
    • 1
  • Eldin E. Karaikovic
    • 1
  • Hyung-Soon Park
    • 2
  • Mark J. Sokolowski
    • 3
  • Li-Qun Zhang
    • 2
  1. 1.Department of Orthopaedic SurgeryNorthShore University Healthcare SystemEvanstonUSA
  2. 2.Rehabilitation Institute of ChicagoNorthwestern UniversityChicagoUSA
  3. 3.Trinity OrthopaedicsOak ParkUSA

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