View Full Version : Marker placement for spinal coordination

01-18-2000, 11:31 PM
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
Email: Rebecca.States@liu.edu

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