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Re: DISCUSSION FORUM ON CONTEMPORARY ISSUES INBIOMECHANICS: Topic 2

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  • Re: DISCUSSION FORUM ON CONTEMPORARY ISSUES INBIOMECHANICS: Topic 2

    Congratulations to Prof. Hatze! After a fairly unprovocative period on
    BIOMCH-L, something to stiffen the sinews (and, therefore, reduce those soft
    tissue submotions!).

    In response to points 1,2 and 5:

    Neglecting other pursuits in musculo-skeletal biomechanics, in clnical gait
    analysis the motion of the body refers to the
    motion of body segments around joints. In that sense then, we describe the
    skeletal motion, with the mean displacement of the soft-tissues in a steady
    state, cyclical, activity being zero relative to the skeleton. Of course,
    the sub-motion of the soft tissues may alter joint kinetics and
    therefore the motion of the skeleton, though the size of these effects may
    be
    small in all but sporting activities.

    In principal, we are able to perform a validation exercise of the
    description of motion derived from surface markers without doing anything
    too dreadful to the subject. I understand that some researchers are using a
    texture matching technique between 2D projections of CT data and images from
    dynamic biplanar
    radiographs, to locate skeletal structure in 3D in treadmill walking.
    They generate results with high levels of accuracy when compared to 3D
    kinematics
    computed from fiducial markers (a relatively
    non-invasive gold standard, perhaps?) . Could we use such techniques to
    verify the
    use of surface markers to describe kinematics or calculate the magnitude of
    our errors?

    Of course, the accurate calculation of joint kinetics would still remain
    elusive, particularly those parts derived from the inertial components.
    Better, perhaps bespoke, anthropometric models are required. MRI is
    providing some of that data, but the availability and cost of this
    measurement may be probibitive to many laboratories. In
    our laboratory, we use 3D ultrasound (optical tracking of a linear array
    probe) to measure muscle morphology in the
    static subject, for clinical purposes. It would be possible to make some
    better estimates of the distribution of muscle volume and therefore muscle
    mass using this technique. Also, we have performed some preliminary work
    measuring bony
    lengths (to within a few mm accuracy, we believe). With optically-guided
    ultrasound, it should be possible to estimate joint centres and calculate
    moment arms (in static conditions) without the skin and soft tissue spoiling
    things (we haven't done this yet!).

    Whether it's ultrasound and/or other techniques, motion analysis needs
    local, relatively inexpensive, adjunctive methods to fill the
    subject-specific knowledge gaps.

    Adam Shortland PhD,
    One Small Step Gait Laboratory,
    Guy's Hospital
    LONDON
    UK
    adam.shortland@virgin.net

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