2010 RWISO Journal - Roth Williams International Society of ...

This is an extremely large error when we are attempting
to locate a THA. Fortunately, it seldom happens that we attempt
to locate a THA from a distance of 50 mm in clinical
practice (Figure 58).
Figure 58 If we try to extend the stylus to the skin to mark a
hinge point from a point located at a far distance from the
skin using Axiograph III, it would result in a very large error.
The fact remains, however, that the greater the distance
between the skin and the stylus, the less accurate are the
marks on the skin (Figure 59). Therefore, we are likely to
make a large error if we use a false hinge axis that deviates
substantially from the THA (Figure 60).
Figure 59 The greater the distance between the skin
and the stylus, the less accurate the marks of
the THA on the skin will be.
Precision mounting
using a false hinge
axis results in a very
large error.
Figure 60 We are likely to create a large error if we use the
false hinge axis, which deviates substantially from the THA.
30 Choi | Hinge Axis: The Need for Accuracy in Precision Mounting Part 2
Next, let us examine the precision mounting system of
the Axiograph III. Figure 61 shows a magnified view of the
highlighted area. The various parts of the highlighted area
are shown in Figure 62. They are, respectively, the side arm
of the upper frame, the flag table attached to the side arm,
the recording arm of the lower frame, and the stylus attached
to the recording arm.
Figure 61 Schematic drawing and
real picture of the stylus area.
Figure 62 Magnified view
The THA is the line that connects the left and the right
styli. It passes through an imaginary hole in the flag table.
The stylus marks the hinge point in red or blue on the graph
of the flag table (Figures 63 and 64).