STP1560

    Plastic Deformation from Edge Loading is Common on Retrieved Metal-on-Metal Hips and Can Be Predicted With Finite Element Analysis

    Published: May 2013


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    Abstract

    Current generation metal-on-metal (MoM) hip bearings have been designed to achieve low contact stress and low in vivo wear rates. Pre-clinical wear testing did show very low wear rates and great promise for young and active patients. However, clinical outcomes have not matched the laboratory tests, with a commonly reported cause of failure being metallosis and/or other adverse tissue reaction to metal wear debris. Analysis of retrieved MoM devices allows evaluation of the effect of in vivo articulation on the bearing surfaces. Large depth-of-field digital microscopy and three-dimensional white light profilometry can be used to study the bearing surfaces to document the wear phenomena that occurred in vivo. Among the surface damage features that are commonly observed on retrieved MoM bearings are gouges, linear damage features that are found on the articular surfaces of femoral heads. In a study of over 100 retrieved MoM bearings of eight contemporary designs, significant linear damage features were observed in all designs and in over 80 % of devices overall. It has been established by other studies that subluxation and reseating of hips occurs during the swing phase of the gait. Our study uses computer modeling of the contact resulting from reseating of the head on the rim to predict the geometry of the plastically deformed features that would be created. Under physiological loading conditions, the modeling predicts narrow, linear zones of plastic deformation on the head. This geometry closely matches the commonly observed linear damage features on retrieved MoM bearings, providing compelling evidence that plastic deformation caused by rim loading occurs in vivo across a wide range of MoM device designs. Laboratory testing protocols developed for MoM bearings should consider the observation of gouge features that appear on MoM retrievals and might be caused by routine in vivo rim loading.

    Keywords:

    metal-on-metal, hip, finite element analysis, arthroplasty, stress, edge loading, replacement, damage


    Author Information:

    McHugh, Dermott
    Thayer School of Engineering, Dartmouth College, Hanover, NH

    Dartmouth Biomedical Engineering Center, Thayer School of Engineering, Dartmouth College, Hanover, NH

    Currier, John
    Thayer School of Engineering, Dartmouth College, Hanover, NH

    Kennedy, Francis
    Thayer School of Engineering, Dartmouth College, Hanover, NH

    Collier, John
    Thayer School of Engineering, Dartmouth College, Hanover, NH

    Van Citters, Douglas
    Thayer School of Engineering, Dartmouth College, Hanover, NH

    McHugh, Dermott
    Thayer School of Engineering, Dartmouth College, Hanover, NH

    Dartmouth Biomedical Engineering Center, Thayer School of Engineering, Dartmouth College, Hanover, NH

    Currier, John
    Thayer School of Engineering, Dartmouth College, Hanover, NH

    Kennedy, Francis
    Thayer School of Engineering, Dartmouth College, Hanover, NH

    Collier, John
    Thayer School of Engineering, Dartmouth College, Hanover, NH

    Van Citters, Douglas
    Thayer School of Engineering, Dartmouth College, Hanover, NH


    Paper ID: STP156020120046

    Committee/Subcommittee: F04.22

    DOI: 10.1520/STP156020120046


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