# Computational Wear Prediction of TKR with Flatback Deformity during Gait
## 4 Discussion  
The purpose of this study was to compare the maximum contact pressure, distribution of contact pressure and wear depth from the flatback gait mechanism against the normal gait mechanism. Unlike the normal gait mechanism, the flatback gait mechanism maintains the knee flexion and maintains the vertical force applied to the knee, so it can be expected that the wear characteristics of the two gait mechanisms will be different.  
When the finite element analysis was performed for 5,000,000 gait cycles, the maximum contact pressure of the flatback gait mechanism decreased as the cycles increased in the 25-50% gait cycle section, unlike the normal gait mechanism (see Figure 13). This reduction in contact pressure causes more contact pressure to be applied to the tibia insert in a specific gait section, resulting in more wear. It can be inferred that the generated wear increases the conformity of the shape of the joint contact surface, so the contact area is widened and the contact pressure is dispersed, resulting in a decrease in the maximum contact pressure. In the maximum wear depth graph, it was confirmed that the maximum wear depth of the flatback gait mechanism was generally greater than the wear depth of the normal gait mechanism in the 25-50% gait cycle section (see Figure 14).  
For the contact pressure distribution, it is important to analyze the difference in the contact area rather than the contact pressure distribution point. The contact pressure distribution area was larger in the case of the flatback gait mechanism, and it can be seen that the contact pressure was also greater in this gait cycle. From this result, we can infer that the increase in the contact pressure region is not the effect of distributing the load, but is due to the increase in the applied contact pressure. Since the simultaneous increase of the contact pressure and the contact area can be judged as an increase in the wear volume, it can be predicted that the wear volume will be greater in the flatback gait mechanism. In relation to this, as shown in Figure 13, the large decrease of the maximum contact pressure in the case of flatback gait mechanism in the 25-45% gait cycle can be analyzed as a phenomenon in which the load is distributed because the contact area is widened due to wear even when the same load is applied.  
The maximum wear depth showed a generally great value after 50% of the gait cycle, just before the swing phase for both gait mechanisms (see Figure 14). This can be thought of as a large increase in the maximum wear depth because the sliding distance increases when the foot is off the ground and the joint rotates freely. In addition, as the maximum wear depth is greater in the 20-40% gait cycle for the flatback gait mechanism, the fact that the maximum wear depth, which is directly related to the wear volume, shows different trends in the two gait mechanisms can be considered as different wear points. Due to this, it can be expected that the shape of the deformed tibial insert and the femoral component will appear differently for the two gait mechanisms. One of the ways to reduce the wear of the knee artificial joint is to increase the conformity of the tibial insert and the femoral component [34,35]. Therefore, if you increase the conformity of the knee joint artificial joint, for this reason, the contact pressure can be reduced, so it can be inferred that the wear depth and the wear volume will decrease. In conclusion, it is necessary to predict wear patterns in consideration of gait characteristics different from those of normal persons in order to  
Figure 14: Comparison of maximum wear depth after 5,000,000 cycles in two gait mechanisms: (a) Normal gait mechanism; (b) Flatback gait mechanism.  
improve the conformity of the femur and bearing during TKR (total knee arthroplasty) in the case of flatback patients.