## 3 Materials and Methods
### CT Acquisition, Segmentation, and Image Reconstruction  
FE models for biomechanical studies are usually constructed by means of patient-specific geometry (X-ray, Tomography, Computerized Axial Tomography (CT), Magnetic Resonance Imaging (MRI)), or by computer-aided design software [9; 11; 40; 41; 42; 43; 44]. Computerized Axial Tomography or CT scan is one of the tests that are commonly used for medical imaging diagnosis [45]. In the present case, two medical CT scans of the same patient (male, 80 kg in weight), obtained five years apart, were conducted. The older CT scan corresponds to the healthy hip joint when the patient was 22 years old, whereas the most recent CT scan corresponds to the hip joint with Cam-type fenoroacetabular impingement (when the patient was 27 years old). In this case, a Philips CT Scanner was used to obtain the CT scans for both hip joints. Its configuration was: 512 \(\times\) 512 matrix size, 168 mm window width, 0.32 mm pixel pitch, 5 mm cutoff pitch, 120 kVp, and 80 mA. Both medical CT scans provided DICOM files (DCM) of the healthy and Cam-type fenoroacetabular impingement patient's hip joints. The segmentation process was conducted with the free 3D software Slicer [46]. To ensure that the cortical and cancellous bone were considered as independent parts of the hip and femur, the segmentation process was based on the threshold values of Hounsfield units (HU). Two different masks were created for the cortical and cancellous bone. A threshold with values that ranged from 700 Hu to 3070 Hu was used for the cortical bone mask. A threshold with a range of values from 150 HU to 700 HU was used for the trabecular bone and cartilage. Smoothing and repairing the defects of the segmentation process was conducted with free MeshMixer software. It generated both models in STL files format [47]. Figure 3 shows the segmentation process using the free 3D Slicer software and the smoothing and repairing of defects, generating the masks of the damaged hip joint using the MeshMixer software. Figure 3a shows the pelvic segmentation  
Figure 2: Steps followed to obtain the FE models from the patient’s CT scan.  
process, whereas Figure 3b shows the pelvic cancellous and cortical bone masks. The femur segmentation appears in Figure 3c, and Figure 3d shows the femur cancellous and cortical bone masks, in which, the Cam-type can be seen.  
In addition, Figure 4a shows a radiograph of the patient at age 27 years. The reduction in the cartilage since the patient was 22 years of age is apparent. Furthermore, it can be seen that contact between the head of the femur and the acetabulum of the pelvis is imminent. It will cause a condition of arthrosis. Figure 4b shows, respectively, the masks obtained for the patient's healthy cartilage and the masks for the damaged cartilage (Figure 4c, obtained recently with the Cam-type) in which a severe reduction in the thickness of the cartilage is visible, especially in the outer areas. This last figure indicates that the cartilage has been damaged and is smaller. Thus, less of the head of the femur is covered by cartilage.  
Figure 4: Reduction of the cartilage: (**a**) radiograph of the patient at age 27, (**b**) masks obtained for the patient’s healthy cartilage and (**c**) masks obtained for the patient’s damaged cartilage.  
Figure 3: Segmentation process and generation of the masks: (**a**) pelvic segmentation, (**b**) pelvic cancellous and cortical bone masks, (**c**) femur segmentation and (**d**) femur cancellous and cortical bone masks (with Cam-type), (**e**) detail of the cam-type on the head of the femur.