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Comparison of the biomechanical effects of posterior and anterior spine-stabilizing implants

European Spine Journal volume 14, pages 445–453 (2005)Cite this article

Abstract

Posteriorly and anteriorly fixed implants for stabilizing unstable spines are available on the market. Differences in the biomechanical behavior of these implant types are not yet fully clear. They were investigated using three-dimensional nonlinear finite element models of the lumbar spine in an intact state, with an anteriorly fixed MACS-TL implant and with posteriorly fixed internal fixators. The bisegmental implants spanned the L3 vertebra, and bone grafts were used with both implant types to replace parts of the two bridged discs. The computer models were loaded with partial body weight and muscle forces simulating standing, flexion, extension and axial rotation. Both implant types have reduced intersegmental rotation for flexion, extension, and axial rotation in the bridged region. The reduction is more pronounced for the MACS-TL implant. The implant type has only a minor effect on intradiscal pressure. Maximum von Mises stresses in the vertebrae are lower for flexion and extension with the MACS-TL implant than with the internal fixator. Very high stresses are predicted for flexion after insertion of internal fixators. For standing and torsion, maximum stresses differ only negligibly between the two implant types. In the period immediately after surgery, patients with osteoporotic vertebrae and who are treated with an internal spinal fixation device should therefore avoid excessive flexion. This study adds new information about the mechanical behavior of the lumbar spine after insertion of posterior and anterior spine-stabilizing implants. This information improves our biomechanical understanding of the spine.

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Acknowledgements

The original element mesh of the L4 vertebra was created by Smit. It is available on the internet at the ISB Finite Element Repository managed by the Instituti Ortopedici Rizzoli. Finite element analyses were performed at the Norddeutscher Verbund für Hoch- und Höchstleistungsrechnen (HLRN) and Zentraleinrichtung Rechenzentrum Berlin (ZRZ). The authors thank M. Fehrmann for assistance with the finite element calculations and Dr. J. Weirowski for editorial assistance. Funding for this study was obtained from the Deutsche Forschungsgemeinschaft, Bonn, Germany (Ro 581/13–3).

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  1. Biomechanics Laboratory, Charité -Universitätsmedizin Berlin, Campus Benjamin Franklin, Hindenburgdamm 30, 12203 , Berlin, Germany

    Antonius Rohlmann, T. Zander & G. Bergmann

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  1. Antonius Rohlmann
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  2. T. Zander
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  3. G. Bergmann
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Correspondence to Antonius Rohlmann.

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Rohlmann, A., Zander, T. & Bergmann, G. Comparison of the biomechanical effects of posterior and anterior spine-stabilizing implants. Eur Spine J 14, 445–453 (2005). https://doi.org/10.1007/s00586-004-0784-3

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  • DOI: https://doi.org/10.1007/s00586-004-0784-3

Keywords

  • Biomechanics
  • Finite element method
  • Internal fixation device
  • Lumbar spine
  • MACS system