# Computational Wear Prediction of TKR with Flatback Deformity during Gait
## 3 Results
### Comparison of Contact Pressure of Normal Gait Mechanism and Flatback Gait Mechanism  
Figure 11 shows the graph of the maximum contact pressure in one gait cycle for the normal gait mechanism and flatback gait mechanism. The major difference between the two gait mechanisms was that in the section after 20% of the gait cycle, there was a section in which the maximum contact pressure decreased in the normal gait mechanism, but the flatback gait mechanism did not exist. In addition, the magnitude of the maximum contact pressure at the start of the gait cycle had a value of 15.89 MPa for the normal gait mechanism, while 23.80 MPa for the flatback gait mechanism was higher than that of the normal gait mechanism. Therefore, during one gait cycle, flatback patients are expected to have a greater depth of wear because they receive higher contact pressure than normal. Figure 11: Comparison of maximum contact pressure in two gait mechanisms: (**a**) Normal gait mechanism; (**b**) Flatback gait mechanism. Figure 10: Tendency of maximum contact pressure: (**a**) present study; (**b**) [PERSON] et al. (reprinted with permission from ref. [11]. Copyright 2011 Elsevier); (**c**) [PERSON] et al. (reprinted with permission from ref. [16]. Copyright 2008 Springer Nature); (**d**) [PERSON] et al. (reprinted with permission from ref. [33]. Copyright 2011 Elsevier). Figure 12 shows the contact pressure distribution of the tibial insert in one gait cycle for the normal gait mechanism and flatback gait mechanism. The contact point was similar in both gait mechanisms, but the contact area showed a difference between the two mechanisms. Until the 60% gait cycle, the contact area of the flatback gait mechanism was 10-20% greater than that of the normal gait mechanism. However, after the 60% gait cycle, on the contrary, the normal gait showed slightly larger values than the flatback gait. This phenomenon can be inferred that the gait mechanism with a greater magnitude of the maximum contact pressure in each phase of the compared gait cycle presses the contact surface with a greater force, which resulted in a greater contact area. In the wear simulation, the contact surface shape of the tibial insert is updated at intervals of 500,000 gait cycles. The maximum contact pressure variation during one gait cycle due to the contact surface shape updated every 500,000 cycles is shown in Figure 13. Overall, as the gait cycle increases, the contact area increases due to wear in both the normal gait mechanism and the flatback gait mechanism, and the maximum contact pressure tends to decrease. However, in the 25-50% gait cycle, the two gait mechanisms show different aspects. In this section, the maximum contact pressure in the normal gait mechanism did not decrease significantly even when the number of gait cycles increased, whereas in the flatback gait mechanism, the maximum contact pressure decreased remarkably as the gait cycles increased. This phenomenon can be predicted that more wear occurs on the contact surface of the knee artificial joint in the case of flatback patients in the 25-50% gait cycle. Figure 12: Contact pressure distribution of tibial insert for normal and flatback gait mechanism. In order to confirm the wear depth in one gait cycle, the graph of the maximum wear depth after 5,000,000 cycles was compared. As shown in Figure 14, the peak value of the maximum wear depth was greater in the normal gait mechanism, but the tendency to maintain the maximum wear depth during the gait cycle was greater in the flatback gait mechanism. The average value of the maximum wear depth during one gait cycle was 1.7953 \(\times\) 10\({}^{-9}\) mm for the normal gait mechanism and 1.8146 \(\times\) 10\({}^{-9}\) mm for the flatback gait mechanism, and there was no significant difference. However, this graph can find meaning in predicting the wear volume for each gait cycle section.