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Marker placement for spinal coordination

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  • Marker placement for spinal coordination

    Hi All,

    We're doing some research on spinal coordination using the Optotrak system
    (small tethered infrared markers). We'd like suggestions on how to mount
    these sensors on the spine so they track spinal motion reasonably.

    We'd like to mount two sensors at each of 5 locations on the thoracic and
    lumbar spine, as well as two on the PSIS, and one marker on the sacral
    spine. The movements we'll measure are flexion, side bending and
    axial rotation through their entire range. Ideally, we'd like to use one
    set of marker placements for all movements, though we're considering using
    one set-up for flexion (maybe with extenders), and a separate one for side
    bending and axial rotation.

    1. One problem is getting good adherance between a rigid body and the spine.
    The shape of the rigid body seems important but we haven't settled on one that
    fits various individuals well. Some people have deeper valleys caused by the
    musculature than others. Also, we want to avoid jiggling the markers due to
    skin movement.

    We've tried:
    placing the markers flat on the skin
    flat rigid pieces of plastic (4-5 cm long and 1 cm wide)
    foam behind those rigid pieces
    a convex shaped rigid body that might fit snugly around a spinous

    2. Another issue is how to mount the markers so they face the plane of the
    cameras. The shape of the spinal curves makes the markers tilt down or up at
    certain spinal levels, and they get obscured at various points within the
    range of motion. Likewise, if the markers are placed on the surface of
    the skin, the musculature obscures them when the subject rotates away from the
    plane of the cameras at all.

    We've considered mounting a styrafoam ball on each rigid body and placing the
    markers so they face the plane of the camera regardless of the direction of
    the skin surface at that point. We also considered using extenders to simply
    move the markers away from the skin and therefore the valleys created by
    the muscle. Neither approach is ideal.

    Your suggestions are welcome!


    Becky States, Marshall Hagins and Rob Gabriel
    Division of Physical Therapy
    Long Island University

    Rebecca A. States, Ph.D.
    Assistant Professor & Research Director
    Physical Therapy, Long Island University

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