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Device Simulates Spine Motions
The spine is the most complex mechanical system in
the human body. With the University of Minnesota in
Minneapolis, Instron (Norwood, MA) is utilizing the
BioPuls™ Multi-Axial Spine Testing System to characterize
the multi-axial dynamism of the backbone. Suchtesting
will help further the understanding of spine kinetics,
simulating precisely the complex, coupled motions typical
of the spine and impact on spina lprocedures. The system
can be used to help evaluate the design of new instruments
and implants that allow a greate rphysiological range
of motion.
The system, which enables six degrees of freedom motion,
uses a “free-endmodel” approach to the testing
of spinal segments and to calculate the finite helical
axis of rotation (FHA). Vertebrae harvested from a pig,
sheep, or human cadaver are loaded into the device and
then subjected to various forces and movements. A set
of specimen cups holds the test “segment”
(two vertebrae with a disc in between) during testing,
and the system cross head can be adjusted vertically
using hydraulic lifts to accommodate different specimen
sizes and different fixturing. A flexion head controls
the three rotational moments of torsion, lateral bending,
and flexion-extension. Dynamism is applied at the top
on the specimen by a flexion head. The lower end, where
a six-axis load cell is used to ensure that the demand
input loads and moments are met, is monitored for reaction.
The centers of rotation are located along the length
of the specimen and as a result, the application of
pure flexion-extension and lateral bending movement
can be made without inducing excessive shear forces. The
unit tests for axial compression, axial torsion, flexion/extension,
lateral bend, anterior/posterior shear, and lateral
sheer, mimicking the full range of motion of which the
spine is capable.
The main goal of the device is to evaluate fixation
(such as fusion or a spinal plate)and disc replacement,
although information about other spinal conditions,
such as scoliosis, can also be gathered. A common experiment
would be to test a segment with its original disc in-tact,
and then replace the disc with an artificial one typical
in disc replacement surgery, and then test the segment
again in the same protocol. The two sets of data would
then be compared, using pro-grams such as Excel or Met
lab, in the hopes of creating more effective therapies.
That information can be bolstered using conventional
methods such as X-rays or MRI scans. Additionally, the
BioPuls can be used for adjacent mechanical studies;
how the altering of one part of the spine impacts the
rest of the system. While a full spine can be fitted
into the BioPuls, five or less segments are used for
effective testing, with multiple configurations allowing
physiologically relevant results.
More Information
For more information on the BioPuls, contact Denise
Papa of Instron Corp at denise_papa@instron.com or visit
http://info.ims.ca/5956-337.
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