PSI - Issue 13

Milena Babić et al. / Procedia Structural Integrity 13 (2018) 438 – 443 E. D. Pasiou, S. K. Kourkoulis , M. G. Tsousi, Ch. F. Markides/ Structural Integrity Procedia 00 (2018) 000 – 000

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The total hip arthroplasty (THA) is a procedure that restores normal function of the hip joint affected by diseases or fracture. The fundamental structure of the total hip prosthesis has remained the same up to the present day, Andriacchi (1997), and orthopaedic implant market continues to increase, Akahori (1998). The THA is a very successful approach and it has become a routine procedure after which the quality of patients’ lives is considerably higher. However, in time, bonds between femoral bone and femoral shaft of the prosthesis may weaken, which can result in prosthesis fracture due to fatigue. Consequently, loosening of the prosthesis is one of the major concerns following the THA, Makarand (2000). According to Marker et al. (2010), failure of the hip prosthesis is not affected by component positioning degree, but it is associated with mean femoral component diameter. Fracture in the femoral component of the total hip prosthesis can occur as a result of the fatigue process. According to Griza et al. (2008), multiple initiation sites can appear, both in the area of tensile stress and in the area of compressive stress due to residual tensile stresses. In real case scenarios according to Capitanu et al. (2012), Mierzejewska and Oksiuta (2014), Hernandez-Rodriguez et al. (2010), the crack usually initiates as a result of bending of the femoral component. According to Chalernpon et al. (2015), static and dynamic loading conditions on the hip prosthesis give similar results in the finite element analysis. 3D scanning is used in a range of fields, including orthopaedics and engineering. It is becoming the most accurate way for creating prosthetics, Vakulenko (2014). In this paper a procedure based on reverse engineering is implemented, where the CAD model of a total hip prosthesis is created by means of 3D scanning. A total hip prosthesis was scanned by a 3D scanner. Based on a point cloud in STL format obtained by scanning, a CAD model was built. Using the obtained CAD model, the finite element models were developed and analyses were carried out. The analyses include a case of a newly implanted prosthesis and three cases of loosened femoral component of the same hip prosthesis.

2. CAD model development based on 3D scanning (reverse engineering)

3D scanning was performed using the ATOS 3D scanner. Prior to scanning the device was calibrated to achieve the needed accuracy. The calibration was conducted on a calibration board shown in Fig. 1a, by sequential scanning of 18 characteristic points and using the GOM Inspect 2016 software. In the first step, the prosthesis specimen was prepared for 3D scanning. Reference point markers were placed on the specimen as shown in Fig. 1b. The reference point markers are necessary for enabling the software to correctly align subsequent scans.

(a) (b) Fig. 1. (a) Calibration process of 3D scanner; (b) sample with reference point markers.

During the scanning process the specimen was fixed on a rotation table as shown in Fig. 2. The specimen was prevented from movement on the rotation table by a clamping device. In eight steps the specimen was rotated by 45°