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The long-term mechanical integrity of non-reinforced PEEK-OPTIMA polymer for demanding spinal applications: experimental and finite-element analysis

Ferguson, Stephen ; Visser, Judith ; Polikeit, Anne

In: European Spine Journal, 2006, vol. 15, no. 2, p. 149-156

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    Titre
    • The long-term mechanical integrity of non-reinforced PEEK-OPTIMA polymer for demanding spinal applications: experimental and finite-element analysis
    Auteur
    • Ferguson, Stephen. Institute for Surgical Technology and Biomechanics, MEM Research Center, University of Berne, Stauffacherstrasse 78, 3014, Bern, Switzerland
    • Visser, Judith. Institute for Surgical Technology and Biomechanics, MEM Research Center, University of Berne, Stauffacherstrasse 78, 3014, Bern, Switzerland
    • Polikeit, Anne. Institute for Surgical Technology and Biomechanics, MEM Research Center, University of Berne, Stauffacherstrasse 78, 3014, Bern, Switzerland
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • European Spine Journal, 2006, vol. 15, no. 2, p. 149-156. Springer-Verlag; http://www.springer.de
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:321420
    Summary
    Polyetheretherketone (PEEK) is a novel polymer with potential advantages for its use in demanding orthopaedic applications (e.g. intervertebral cages). However, the influence of a physiological environment on the mechanical stability of PEEK has not been reported. Furthermore, the suitability of the polymer for use in highly stressed spinal implants such as intervertebral cages has not been investigated. Therefore, a combined experimental and analytical study was performed to address these open questions. A quasi-static mechanical compression test was performed to compare the initial mechanical properties of PEEK-OPTIMA polymer in a dry, room-temperature and in an aqueous, 37°C environment (n=10 per group). The creep behaviour of cylindrical PEEK polymer specimens (n=6) was measured in a simulated physiological environment at an applied stress level of 10MPa for a loading duration of 2000hours (12weeks). To compare the biomechanical performance of different intervertebral cage types made from PEEK and titanium under complex loading conditions, a three-dimensional finite element model of a functional spinal unit was created. The elastic modulus of PEEK polymer specimens in a physiological environment was 1.8% lower than that of specimens tested at dry, room temperature conditions (P<0.001). The results from the creep test showed an average creep strain of less than 0.1% after 2000hours of loading. The finite element analysis demonstrated high strain and stress concentrations at the bone/implant interface, emphasizing the importance of cage geometry for load distribution. The stress and strain maxima in the implants were well below the material strength limits of PEEK. In summary, the experimental results verified the mechanical stability of the PEEK-OPTIMA polymer in a simulated physiological environment, and over extended loading periods. Finite element analysis supported the use of PEEK-OPTIMA for load-bearing intervertebral implants