Medical Engineering & Physics
Volume 29, Issue 10 , Pages 1089-1095, December 2007

The number of screws, bone quality, and friction coefficient affect acetabular cup stability

  • Jui-Ting Hsu

      Affiliations

    • Institute of Biomedical Engineering, National Cheng Kung University, Tainan 701, Taiwan, ROC
    • Biomechanics Laboratory, Division of Orthopedic Research, 200 First Street SW, Rochester, MN 55905, USA
    • ,
  • Chih-Han Chang

      Affiliations

    • Institute of Biomedical Engineering, National Cheng Kung University, Tainan 701, Taiwan, ROC
    • ,
  • Heng-Li Huang

      Affiliations

    • Dental School, College of Medicine China Medical University, Taichung 404, Taiwan, ROC
    • ,
  • Mark E. Zobitz

      Affiliations

    • Biomechanics Laboratory, Division of Orthopedic Research, 200 First Street SW, Rochester, MN 55905, USA
    • ,
  • Weng-Pin Chen

      Affiliations

    • Department of Biomedical Engineering, Chung Yuan Christian University, Chungli 320, Taiwan, ROC
    • ,
  • Kuo-An Lai

      Affiliations

    • Orthopaedic Department, National Cheng Kung University Medical Center, Tainan 701, Taiwan, ROC
    • ,
  • Kai-Nan An

      Affiliations

    • Biomechanics Laboratory, Division of Orthopedic Research, 200 First Street SW, Rochester, MN 55905, USA
    • Corresponding Author InformationCorresponding author. Tel.: +1 507 538 1717; fax: +1 507 284 5392.

Received 31 March 2006; received in revised form 7 November 2006; accepted 10 November 2006. published online 28 December 2006.

Abstract 

One of the major causes of loosening of cementless acetabular cup implants is insufficient initial stability. This study used three-dimensional finite element models of the pelvis and acetabular components to investigate the effects of the number of screws, bone quality, and friction coefficient of the acetabular cup on the initial stability under normal walking. A commercially available hemispherical acetabular cup with five screw holes was used as the default model. The stiffness of the pelvis and the friction coefficient of the cup were systematically varied, within a realistic range, to assess the initial stability of the acetabular cup. The simulations showed that the inserted screws provide only a localized reduction in the relative micromotion between the cup and pelvis therefore inserting several screw closed together might not be useful. Changes in the pelvic stiffness have a non-linear effect on the initial stability of acetabular cup and the subchondral bone provides good support for fixation of the cementless cup. The friction coefficient of the acetabular cup plays a limited role, comparing with the factor of bone quality, in resisting relative micromotion in the cup–pelvis interface.

Keywords: Acetabular cup, Initial stability, Screw fixation, Bone quality, Coefficient of friction, Finite element method

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PII: S1350-4533(06)00234-7

doi:10.1016/j.medengphy.2006.11.005

Medical Engineering & Physics
Volume 29, Issue 10 , Pages 1089-1095, December 2007

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