1. Tribology Research Institute, School of Mechanical Engineering, Southwest Jiaotong University, Chengdu 610031, China; 2. The General Hospital of Western Theater Command of PLA, Chengdu 610083, China
Abstract：[Objective] After total hip arthroplasty, the contact stress spot between the femoral head and the liner can easily move from the liner's inner surface to its contour edge under different gaits, resulting in edge loading (EL) at the liner edge. The occurrence of EL will reduce the mechanical properties of the liner, increase the wear of the hip prostheses, and reduce the service life of hip prostheses and the quality of life of patients. EL is related to the prosthetic mounting position, geometric design, and patient motion status. This study aimed to investigate the contact mechanics and EL of elevated-rim liner edges at different gaits and mounting positions to guide clinical prosthesis mounting and postoperative rehabilitation of patients. [Methods] In this study, we developed a finite element analysis model of elevated-rim liner contact mechanics and hip joint EL under gait loading based on a metal-on-polyethylene contact bearing. Four gaits (normal walking, ascending stairs, descending stairs, and deep squatting) common to the patient's daily life were used as kinetic inputs to the finite element model. The model considered the radiographic inclination and anteversion of the acetabular cup at relatively extreme positions and the elevated rim of the liner at different orientations in human body. After finite element mesh sensitivity analyses, mechanical results such as contact stresses, EL, EL duration, equivalent plastic strain, and volume of the equivalent plastic strain of the elevated-rim liner were investigated. [Results] The finite element results showed that the maximum surface normal contact stresses on the inner surface of the elevated-rim liner under normal walking, ascending stairs, descending stairs, and deep squatting gaits were 11.60, 12.44, 11.96, and 12.07 MPa, respectively, with no significant difference. The maximum surface contact stresses on the liner where EL occured were 3.29, 3.40, 4.85, and 4.45 MPa, respectively. The ratios of the EL duration to the gait cycle were 14%, 34%, 50%, and 54%, respectively. The maximum equivalent plastic strains were 2.82×10-4, 4.89×10-4, 5.31×10-4, and 6.56×10-4, respectively, and the volumes where the equivalent plastic strains occurred were 37.07, 65.01, 67.66, and 150.00 mm3, respectively. [Conclusions] The equivalent plastic strain of the elevated-rim liner, the volume in which plastic deformation occurs, and the EL of the elevated-rim liner and its duration all increase with the radiographic inclination and anteversion of the acetabular cup. Compared with the other three gaits, the deep squatting gait is more likely to cause plastic deformation of the liner and consequently the most damage to the liner. Therefore, patients should avoid movements with high flexion after total hip arthroplasty. Placing the elevated rim of the liner on the posterosuperior side of the body and the radiographic inclination of the acetabular cup no less than 50° can avoid EL and significantly reduce the plastic strain of the liner. Total hip arthroplasty should consider not only the patient's postoperative impingement-free range of motion but also the mechanical condition of the patient's postoperative prostheses, thus prolonging the life of the prostheses.
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2024, Vol. 64 
