gms | German Medical Science

Deutscher Kongress für Orthopädie und Unfallchirurgie
74. Jahrestagung der Deutschen Gesellschaft für Unfallchirurgie
96. Tagung der Deutschen Gesellschaft für Orthopädie und Orthopädische Chirurgie
51. Tagung des Berufsverbandes der Fachärzte für Orthopädie und Unfallchirurgie

26. - 29.10.2010, Berlin

The influence of multilevel lumbar disc arthroplasty on spine kinematics and facet joint forces – a finite element study

Meeting Abstract

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  • H.-J. Wilke - Universität Ulm, Institut für Unfallchirurgische Forschung und Biomechanik, Ulm, Germany
  • H. Schmidt - Universität Ulm, Institut für Unfallchirurgische Forschung und Biomechanik, Ulm, Germany
  • F. Galbusera - Universität Ulm, Institut für Unfallchirurgische Forschung und Biomechanik, Ulm, Germany

Deutscher Kongress für Orthopädie und Unfallchirurgie. 74. Jahrestagung der Deutschen Gesellschaft für Unfallchirurgie, 96. Tagung der Deutschen Gesellschaft für Orthopädie und Orthopädische Chirurgie, 51. Tagung des Berufsverbandes der Fachärzte für Orthopädie. Berlin, 26.-29.10.2010. Düsseldorf: German Medical Science GMS Publishing House; 2010. DocIN12-1103

DOI: 10.3205/10dkou086, URN: urn:nbn:de:0183-10dkou0867

Veröffentlicht: 21. Oktober 2010

© 2010 Wilke et al.
Dieser Artikel ist ein Open Access-Artikel und steht unter den Creative Commons Lizenzbedingungen (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.de). Er darf vervielfältigt, verbreitet und öffentlich zugänglich gemacht werden, vorausgesetzt dass Autor und Quelle genannt werden.


Gliederung

Text

Objective: Total disc arthroplasty (TDA) has been successfully used for monosegmental treatment in the last few years. Therefore, more and more surgeons started to use artificial discs for multisegmental approaches. However, already two-level lumbar TDA led to controversial clinical results. Therefore, the application of three or even four-level TDA is under heated debate. We hypothesize that: (1) the more artificial discs are implanted, the stronger the increases in spinal mobility and facet joint forces; (2) deviations from the optimal implant position lead to strong instabilities. Therefore, we investigated these hypotheses in finite element analyses.

Methods: A three-dimensional non-linear finite element model of the intact L1-L5 human lumbar spine was created. Additionally, finite element models of the L1-L5 region implanted with multiple Charité artificial discs at different levels were created. The models represented different possible clinical conditions ranging from two to four-level TDA, and took into account possible misalignments in the antero-posterior direction of the artificial discs. All these models were exposed to an axial compression preload of 500 N. Pure unconstrained moments of 7.5 Nm were subsequently applied to simulate flexion and extension.

Results and Conclusions: For central implant positions and the loading case extension, a strong increase of the range of motion (from 51% for two implants to 91% for four implants) and a marginal increase of the facet joint forces (from 24% for two implants to 38% for four implants) were calculated after multilevel TDA. In flexion, the models predicted a motion decrease of 5% for two implants, 11% for three implants and 8% for four implants compared to the intact lumbar spine. Some of the artificial disc models led also in flexion to small facet joint forces with a maximum value of 17 N. For both flexion and extension, the motion and the facet force alterations between the intact model and all instrumented lumbar spines occurred mainly at the implanted segments. Generally, posteriorly placed implants led to a better representation of the range of motion calculated for the intact lumbar spine. However, lift-off phenomena between the core and the implant endplates were observed in some extension simulations in which the artificial discs were anteriorly or posteriorly implanted.

From this study, it can be concluded that multilevel TDA leads to significant increase of both spinal mobility and facet joint forces. The more artificial discs are implanted, the stronger these increases can be expected. Deviations from the optimal implant position lead to unfavorable kinematics, to high facet joint forces and even to lift-off phenomena. Therefore, multilevel TDA should, if at all, only be performed in appropriate patients with good muscular conditions and by surgeons that can ensure optimal implant positions.