## 4 Discussion  
In this study, the geometrical changes had a primary role in the determination of the efficiency of the overall evaluation system. In order to check the result of donning simulation, a special process for taking the MRI data wearing the developed sockets is necessary. This process is a burden for the subjects, so we limited the number of subjects when we applied to the ethical committee of our university. Even though the number of subjects participating in the study is low, it is enough to accomplish the geometrical changes observation objective. In the cases where geometrical changes occurred, the correlation coefficient value was high in most cases. However, in most cases, low differences of the volumetric value occurred between simulations and measurements. During the complete donning process, a higher deformation was observed in the fat part. The deformation of the fat part represented almost 70% of the total deformation and the changes were mostly in the distal area where the muscle volume was low. The effects of the mean muscle density on deformation were more pronounced than those for fat and the lower volume of the muscle allowed the fat to deform in an easier manner. Figure 8: Variations of the volumes of deformed soft tissue for total soft tissue, fat and muscle. (**a**) Results for subject A with the MCCT socket. (**b**) Results for subject A with the UCLA socket. (**c**) Results for subject B with the MCCT socket. (**d**) Results for subject B with the UCLA socket. (**e**) Results for subject C with the MCCT socket. (**f**) Results for subject C with the UCLA socket. The simulation results from subject B showed a unique pattern of deformation based on the hypothesis that the fat volume decreased by 21.03% and 15.18%, respectively, in both the proximal and distal areas of the UCLA socket. The increased muscle-fat volume ratio in the residuum most likely affected the deformation because the density of each material affected the movement of the fluid inside the residuum. Subject B had the highest soft tissue volume among all the tested subject residuum values. As a result, the volume of the fat in the distal area has not significantly changed during the complete donning process. Even though subject B is the shortest in height among the others, the diameter of the residuum of subject B is the highest. There is no significant difference in the comparison of the simulation and measurement results for both sockets and a high-correlation coefficient value is estimated for these sets. Subject B has a history of wearing the socket. In this respect, the muscle has become used to the local environment and the elasticity of the residuum is likely to be low and tends to shrink during its insertion into the socket. Figure 9 shows the error distributions of soft tissue volumes between FEA and IP measurements in every layer for each subject with and without sockets. The differences detected in the measured and simulated values are most likely caused by the fact that in the simulation cases, the muscle and the fat part are considered as one entity, while in real cases both parts are connected to each other. Furthermore, the internal fat inside the muscle was ignored in simulations, which led to fat volume decreases. The highest error observed in the distal area of all part models is shown in Figure 10. Specifically, the average errors for the distal areas were respectively equal to 2.88%, 9.33%, 11.92%, 1.04% 13.07%, 13.1%, 1.26%, 12.02% and 20.09%, for subjects A, B and C, without the socket and with the MCCT and UCLA sockets. The error in the proximal area was 32% lower than the average distal area in every model. A significant error was observed in the distal area, most probably because the simulation model was designed from a visually clear, large planar area in the distal end, while the IP measurement was based on the differentiation of a small area which was very precise.