In-vitro Wear Test and Computational Wear Prediction of Total Hip Replacement in China

The wear particles of hip prosthesis will cause osteolysis, which in return triggers aseptic loosening in the prosthesis itself. It is reported that one of the major reasons for revision total hip replacement is wear and the aseptic loosening caused by it. Under such a background, the pre-clinical evaluation on wear performance of hip prosthesis is becoming increasingly important. Currently, the major approaches of the pre-clinical wear assessments are the in-vitro wear test and the computational simulation. Compared with other countries, the domestic pre-clinical wear study of hip prosthesis is in the primary stage where there are very few articles on the above two approaches. Therefore, it is very important to understand the basic research status of friction and wear of hip prosthesis in China. This article firstly compared the kinematic and dynamic input of gait curves that are used in domestic hip wear assessments with the Chinese measurement gait curves. Then this article summarized, compared and analyzed the results from both domestic in-vitro simulator test and the computational simulation. And lastly this article discussed the limitations and future development directions of the hip pre-clinical wear assessments. The main findings were: 1) The gait motion curves of the Chinese were similar to the Western. The main difference lied in the gait joint force curves. And the Chinese measurement curves cannot be directly used in hip wear evaluate tests as the measurement method of hip joint force needs to be improved. 2) The domestic and the international research findings of in-vitro wear tests conducted according to the ISO 14242-1 standard were similar but the results according to other testing standards (e.g., ISO 14242-3) showed differences. This meant the accuracy of domestic in-vitro wear test results were influenced by the testing standards and testing equipment. 3) The simplified dynamic curves according to the ISO 14242-1 can be input to the finite element model to reduce the computational time. The wear rates of the domestic computational simulation were generally lower than those of the in-vitro wear tests. As a result, the accuracy of domestic computational wear models needed further improving. There were also some limitations on the current domestic wear assessments and researches. The first one was the gap between the Chinese standards and international standards. Some extreme conditions like third body wear, edge load and micro separation were not considered in current Chinese standards. Secondly there was still no gold standard on extraction of wear debris. Thirdly it was difficult to consider simultaneously the factors from patients, doctors and manufacturers that impacted on the wear performance of hip prosthesis. In order to catch up the international wear research progress of hip prosthesis, the future domestic pre-clinical wear assessments should focus on: 1) Building the national wear assessment standard that is appropriate for domestic patients; 2) Improving the extraction method of wear debris; 3) Promoting the accuracy of computational model by adopting more realistic dynamics inputs and by optimizing the wear models; 4) Combining the approaches of finite element analysis and force dependent kinematics to study the impact of patients’ situations, doctor’s techniques, products parameters on the wear performance of hip prosthesis.