Summary
Summary A transducer for measuring threedimensional segmental spinal motion was designed
to directly measure dynamic rotations (Rx, Ry and Rz) about three orthogonal axes
using an array of liquid metal strain gauges (LMSGs). The configuration of the LMSG
array results in differential length changes due to segmental spinal motion. In vitro
calibration utilized transducer attachment to Steinmann pins implanted into the dorsal
spinous processes of anatomical spinal segments. The response of the LMSGs approximated
linearity (R2 ≥0.980) over the calibrated ranges of angular displacement (i.e., ± 5°). On average,
artifactual mechanical noise of the LMSGs was <3% of the signal recorded during locomotion.
The minimum resolution of the transducer was 0.07 degrees of flexion-extension, 0.46
degrees of lateral bending, and 0.56 degrees of rotation. Average resistive force
for all transducers was 0.31 ± 0.05 Nm at the neutral articular position (0°) and
0.51 ± 0.03 Nm at 5° of flexion. Clinically, the modest mechanical resistance of the
transducers did not affect spinal mobility nor locomotion. In vivo application of
the transducer was demonstrated at thoracolumbar and lumbosacral spinal segments in
horses treadmill locomotion. The transducer was designed and tested on an equine model,
but may be adapted for other quadrupeds. The dynamic and continuous measure of three-dimensional
in vivo segmental spinal motion will provide an important new perspective for evaluating
normal and altered spinal motion.
A technique was developed for directly measuring threedimensional segmental spinal
motion in the thoracolumbar and lumbosacral spinal segments in horses during treadmill
locomotion. The dynamic and continuous measure of three-dimensional in vivo segmental
spinal motion will provide an important new perspective for evaluating normal and
altered spinal motion associated with back problems.
Keywords
Kinematics - spine - liquid metal strain gauge - equine
