PhD Fekete - SZIE version - 2.2 - Szent István Egyetem

Results
4.2.2. Discussion and interpretation of the results
Let us first look at the magnitude and the pattern of the sliding-rolling ratio of the different
prostheses and then at the tibiofemoral contact forces. The calculation of the sliding-rolling is
considered on both sides of the condyles (lateral and medial) and involves the slip in every
direction (spatial).
In the case of the SZIU prototype model (Figure 4.6), both of the lateral and medial sides start
from a positive sliding-rolling ratio of 0.2. The functions gradually increase with occasional
irregularities to 0.42 at the medial side and 0.38 at the lateral side.
The irregularity during the motion is originated to the contact of the complex geometries. These
mapped geometries are numerically approximated curves, thus their smoothness is also a factor
that can cause less smooth functions. In Figure 4.16, an approximated prosthesis curve is visible
from the sagittal view. The original analytical curve is represented with continuous line, the
tangents with dotted lines, and the numerical curve with a dashed line.
Figure 4.16. Approximated prosthesis curve
As the two bodies establish a contact and they start moving along these curves, the sharp
approximating lines (Figure 4.16 a-b) may cause small jumps, skips on the bodies, which
appear mainly on the sliding-rolling functions.
If we neglect these irregularities, the increment shows closely linear growth. With regard to the
kinetics, namely the tibiofemoral force (Figure 4.7), between the condyles, the evolution of the
force can be described as closely linearly increasing, with a maximum of 4.5-8.5 times of the
BW.
The Biotech TP and the TP P/S models (Figure 4.8 and Figure 4.10) are from the same
manufacturer. They have quite similar characteristics both in their kinematics and their kinetics.
In both cases the sliding-rolling evolution is quite smooth along the complete segment (0˚ to
120˚) compared to the SZIU model which is more hectic. However the tibiofemoral force of the
TP model (Figure 4.9) is half times lower compared to the TP P/S force (Figure 4.11).
The sliding-rolling curves regarding the TP and TP P/S start approximately from 0.3. From 40-
60˚ of flexion angle, the TP and TP P/S functions begin to increase until they reach the
maximum sliding-rolling ratio, 0.7 in the case of the TP model and 0.725 in case of the TP P/S
on both medial and lateral side.
The BioMet Oxford model (Figure 4.12) has lower sliding attribute, since between 20-60˚ of
flexion angle it only reaches the value of 0.2-0.22. It has also the feature of closely linear
growth, with minor irregularities, on both sides.
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