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

a) Guide design 1 b) Guide design 2 c) Guide design 3
Figure 1: The three different guide designs created to drill four holes in the distal femur.
Based on these stability parameters, two quality scores are then defined to compare
different guide designs on a limited scale:
and represent respectively the translational and rotational stability
behaviour of full contact surface on a cube, which is the optimal stable situation. The
quality score and are then limited over a range of 0 to 10, where a score of 10
represents a perfectly stable contact.
2.2 Guide design
Three guides were designed to fit on a distal femur in 3-matic ® (Materialise NV,
Leuven, Belgium). The designs were created to drill four pins in the distal femur, as
done when performing a total knee arthroplasty (TKA). As can be seen in Figure 1, the
guides differ in position of the base plate: the first design shows little coverage, the
second design uses the femoral surface visible in a standard TKA for support and the
third design creates a cap over a large part of the femur not taking soft tissue or incision
constraints into account. Expected is that this variation in baseplate contact will result in
a different feeling of stability when positioned on the femoral surface.
2.3 Experiment
All guides and a model of the distal femur were created using additive manufacturing
(selective laser sintering using polyamide material). A fit test was performed where
multiple users were asked to manipulate the different guides on the bone model to
assess the haptic feeling of stability. With respect to possible movement, the users had
to assign a score between 1 and 5 which reflected the feeling of stability they had for a
specific guide. The score charts presented to them are shown in Table 1 and Table 2.
Table 1: Score chart presented to the users during the fit test with respect to translational stability
of the guide.
1 2 3 4 5
Translation in all
directions possible
Slight translation
(in one direction)
(5)
Doesn’t slide