ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

a pure moment load of 7.5 Nm to simulate flexion, extension as well as axial rotation
and lateral bending to the left and to the right. 3 The follower load approach allows simulating
pure compression with 500 N. 4,5
Figure 1: The FE model of the L3-L4 segment is built of simple geometry primitives to enable robust,
automatic, parameterized model generation.
5. PARAMETERS & SAMPLING
Instead of assuming a fixed set of constant parameters, we assigned a probability distribution
to each of the model’s 40 geometry parameters (for instance, disc height,
end plate widths and depths, facet alignment, pedicle angles, etc.; Fig. 2). Whenever
possible we determined the distributions from available data in the literature; otherwise
we had to estimate. 6–8 We then drew a representative sample of size 500 from the
hereby defined “population” by generating FE models using Latin Hypercube Sampling
9,10 and computing the model response for all “observations.”
Figure 2: Instead of a single fixed value, each of the 40 geometry parameters (only six shown) assumes
different values depending on the assigned probability distributions.
6. UNCERTAINTY ANALYSIS
Now we can compute statistics to quantify the uncertainty in the model response: As