Finite element analysis of stress around a sternum screw used to prevent sternal dehiscence after heart surgery

R. S. Jutley, Michael Andrew Watson, David William Laurence Hukins, Duncan Eoin Thomson Shepherd

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    Abstract

    The sternum screw has been proposed as a means of preventing sternal dehiscence, following heart surgery, by increasing the contact area between the wire used to close the median sternotomy and the surrounding bone; as a result, the contact stress is reduced. A finite element model was constructed of a cylindrical wire or screw passing through a block of sternum which consisted of cancellous bone sandwiched within a cortical shell. The thickness of the cortical shell and the material properties of bone were varied between reasonable values. The stress distribution in the sternum was calculated for each model when the wire was subjected to a tension (250 N) which would be required for six wires to withstand a strong cough (40 kPa). Results were validated by comparison with a simple analytical model in which the bone and wire were considered incompressible. They show that the screw reduces the contact stress to almost one-seventh of its value when wire is used alone. Contact stresses are especially high if the cortical shell is thin. The high stress in the bone around a screw falls off within a few millimetres. As a result, no problems are anticipated in placing six screws in each half-sternum so that the sternotomy may be closed with the usual six wires.

    Original languageEnglish
    Pages (from-to)315-321
    Number of pages6
    JournalProceedings of the Institution of Mechanical Engineers. Part H, Journal of Engineering in Medicine
    Volume216
    Issue number5
    DOIs
    Publication statusPublished - 2002

    Keywords

    • bone
    • dehiscence
    • finite element analysis
    • screw
    • sternotomy
    • sternum
    • MEDIAN STERNOTOMY
    • MIDLINE STERNOTOMY
    • CORTICAL BONE
    • CLOSURE
    • COMPLICATIONS

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