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

Table 2: Score chart presented to the users during the fit test with respect to rotational stability of
the guide.
1 2 3 4 5
Rotations in all
directions possible
Slight rotations
(in one direction)
Doesn’t rotate
Table 3: Results of the analysis of the different designs using the computational model.
TT QT Mean TR Mean QR Max TR Min QR
Guide design 1 2.43 3.23 6.78 1.16 7.62 1.03
Guide design 2 2.09 3.75 4.44 1.77 4.73 1.66
Guide design 3 1.25 6.26 1.94 4.05 2.03 3.87
3. RESULTS
3.1 Computational model
The guide designs were analysed using the computational model implemented in
Matlab ® (v. R2011a, The MathWorks Inc., Natick, Massachusetts, USA). The resulting
quality scores are listed in Table 3, where the translational quality scores are listed in
the second column. Looking at these scores, it is to be expected that the first guide
design will be the least stable, where the second will react more stable with respect to
translation. The third guide design should show the least response to a translational
movement.
As the guides are created to guide the drilling of four holes, four possible target points
can be identified as the centre points of the created drill cylinders. From equations (3-5)
it then follows that four different rotational quality scores can be found for one guide
design. Table 3 lists both the maximal and mean rotational stability parameter and
respective quality score of each contact configuration. The maximal rotational stability
parameter reflects the worst-case target point per guide. These scores suggest that the
first guide will be the least stable one. The third guide is predicted to be most
constrained to a rotational movement and the second guide is situated in-between.
3.2 Experiment
During the experiment, ten persons were asked to fit the different guides on the bone
model and manipulate the guide to perceive a feeling of stability. They each filled out
the score chart shown in Table 1 and Table 2. Figure 2 displays the results of this
experiment for the three guide designs. A maximal score was assigned to the third guide
design by every user, for both translation and rotation. The first and second design was
perceived as less stable by all users, where the first design was marked as the least
stable.