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  • Mechanical Testing of Lumbar Specimens

    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,

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    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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