## 3 Results
### Comparison between Standard and Custom Model  
The specific model of the patient was then compared with a standard model [30], which has a greater level of detail at the articulation level. It also presented a schematization of the human muscular system that would require more data with respect to the CT scan, in order to determine the insertion points of each individual muscles. For this reason, it tends to be carried out only when it is actually necessary. To compare the two models (standard and custom) it was necessary to adapt the standard model to the case study by unifying the marker nomenclature. Subsequently, the scaling phase of the standard model was carried out, which was the operation by which it was possible to make the standard model coincide with the markers relating to the analysis of the patient's movement. An effective scaling of the model was usually considered to be when the error was less than 20 mm. Six Gait Analyses (Gait_0, Gait_1, Gait_2, Gait_3, Gait_4, Gait_5) were analysed for the case study. As described in Figure 8, two Gait Analyses were required to obtain a standard model that represented the patient's movement. In particular, Gait_0 (Dynamic analysis) and Gait_5 (static analysis) were used to rescale the standard model. To resize a model, it was necessary to collect data from the subject in a static pose (Gait_5), measure the subject's specifications and related body segments also using the position of the markers and add the functional joint centres from a dynamic test (Gait_0). Because they were used for calibration, these two gait analyses were not considered for the following comparison. Gait_2 and Gait_4 were discarded because they presented problems in marker definition. Finally, Gait_1 and Gait_3 were the two gait analyses used to study the motions applied both to the standard and patient-specific models.  
Figure 8: Flowchart of comparison between standard and custom model.  
Once an adequate standard model scaling was obtained, the two models were compared by performing the inverse kinematics on the movement data obtained by stereophotogrammetry. For comparison, the following error parameters provided for each frame:  
* Total Square Error (TSE)
* Root Mean Square Error (RMSE)
* Maximum Error (ME).  
Tables 1 and 2 contain the mean, maximum value and standard deviation as a function of each motion analysis.  
The software reported the Total Square Error for the worst markers of each frame analysed. The average value, the maximum value and the standard deviation were calculated in order to understand the trend of the markers that were less adherent to the gait analysis for each type of error, both for the Standard model and the Patient-Specific model. Finally, the variation between maximum errors and standard deviation in all three errors were calculated. It could be observed that the patient-specific model had a maximum error that spanned from 12.6% to 26.6% less than the maximum error of the standard model for Gait_1, and was between 7% and 15% less for Gait_3. Concerning standard deviations, it was observed that for both cases, the patient-specific model has half the values of the standard model. In conclusion, from the comparison of the two models, it was found that the customized model was the one that usually had the lowest maximum error and that it was more constant having a usually lower standard deviation, making it preferable to the scaling of the standard model. Moreover, the customized model took into account possible bone deformities or joint placements that the standard model did not consider.