Abstract: BACKGROUND: In hip arthroplasty, placement of the acetabular cup using only the acetabular anatomy will change the direction of the functional acetabular cup. Computer navigation for hip arthroplasty can improve the accuracy of prosthesis placement.  
OBJECTIVE: To simulate the operation, simulate the stress size and area of the acetabular cup, and plan the placement direction of the acetabular cup in hip arthroplasty combined with the pelvic tilt angle to explore the influence of the pelvic tilt angle on the stress distribution of the acetabular prosthesis in hip arthroplasty using finite element model.
METHODS: X-ray and CT data of the pelvis in six cases (marked A-F) were collected. The ABAQUS 6.14-4 (SIMULIA Inc., French) was used to construct hip models. Six models were established to simulate hip arthroplasty with the front pelvic plane in the supine position as the coordinate plane. According to the pelvic tilt angle in the standing position, for those with pelvic tilt angle ≤ -10° and pelvic tilt angle > 10°, the reference plane of prosthesis implantation was adjusted to establish nine models, which were divided into pre-adjusted models: A(-14°), B(-29°), C(11°); post-adjusted models: Aa(-7°), Bb(-18°), Cc(1°); normal models: D(-8°), E(-2°), F(-9°). In the finite element solving software, constraint fixation simulated the standing on one foot. Joint loading was loaded at the sacroiliac joint, pubic symphysis and greater trochanter. The maximum Von Mises stress distribution of the acetabulum, acetabular cup, and lining of each model were compared.  
RESULTS AND CONCLUSION: (1) Model B showed non-convergence and model A showed non-convergence tendency; model B showed convergence with the supine anterior pelvic plane coordination adjusted. In the nine models, the maximum von Mises stress of the acetabulum was 4.9 MPa in model Cc. The minimum stress was 1.07 MPa in model D. The maximum stress of the acetabular cup was 29.87 MPa in model Bb. The minimum stress was 17.21 MPa in model D. The maximum stress of polyethylene liner weight-bearing was 12.45 MPa in model Bb. The minimum stress was 5.21 MPa in model D. The weight-bearing area was located at the middle and upper parts of the acetabulum. (2) The models of the pelvic tilt angle of -14°, -25°, and 11° in the standing position showed maximum values of von Mises stress than the models of -10° < pelvic tilt angle ≤10°. The stress was near the values of models of -10° < pelvic tilt angle ≤10° after adjusting the anterior pelvic plane coordination in the model pelvic tilt angle of -14°, indicating that pelvic tilt angle beyond the range of -10° and 10° is a risk factor for wear and dislocation after total hip arthroplasty. The reset of the anterior pelvic plane in the case of increased pelvic retroversion can reduce the complication in total hip arthroplasty.

Key words: total hip arthroplasty, three-dimensional reconstruction, hip prosthesis, pelvic tilt angle, finite element analysis