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Tsantrizos, Anthony
09-30-1996, 05:12 AM
Dear Biomech-L readers,

I have been involved in mechanical testing of cadaveric specimens (L1-S1),
looking at the three-dimensional primary stability provided by lumbar
interbody fusion implants. I tested my specimens in three movements (axial
rotation, flexion/extension and side bending), and have produced the typical
sigmoid shaped load-displacement curves with hysteresis. Usually, to
quantify the segmental stiffness provided by the implant, average segmental
stiffness is compared (e.g. +/- 8 Nm load amplitude). However, other methods
can be used instead:

(1) Fit a third order polynomial to the sampled points and calculate
stiffness at either :

(a) At the neutral zone, since the stiffness provided here is
more by the implant than the ligaments
(b) At the points of highest/lowest moments, since this is the
maximal stiffness of the motion segment

(2) The overall angular displacement produced by the highest/lowest
load amplitude, since this may be a more relevant measurement in terms of
the actual remaining segmental mobility.

I am looking for any suggestions or comments as to what would better assess
the stability of the motion segment. I will be posting a summary of the
postings.

Thank you,

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Anthony Tsantrizos M.S.
Orthopaedic Research Laboratory
Royal Victoria Hospital
687 Pine Avenue West Room L4.55
Montreal, Quebec
Canada H3A 1A1

Tel. (514) 842-1231 ext. 5382
Fax. (514) 843-1699
E-Mail. atsan@orl.mcgill.ca
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