Evaluation of stress-strain state of the femoral endoprosthesis component with a non-standard cone size and adapter for its standardization

Abstract

This paper presents the results of biomechanical modelling of the "femur–implant" system under condition of non-standard cone size and addition of the developed hip replacement adapter. One of the most effective treatment methods for diseases and injuries of the hip joint is total hip replacement. Expansion of indications for total hip replacement led not only to an increase in the percentage of implants, but also to an increase in the number of recorded complications. The leading position among complications is occupied by aseptic instability of the endoprosthesis components. With isolated reimplantation of the endoprosthesis cup and the friction pair “head–liner”, orthopedists are faced with the problem of non-standard sizes of the neck cone of the stem. This leads to the need for extraction of stable femoral components and a significant decrease in the effectiveness of the technique. To solve this problem, we developed an adapter, which is shaped as a truncated cone. The inner diameter of the adapter corresponds to the outer diameter of the non-standard cone, and the outer diameter of the structure has standard size. Biomechanical modelling methods were used to introduce this development into practical medicine. This paper presents stages of creating biomechanical models of the "bone–implant" system. Biomechanical modelling is carried out in the Ansys Workbench software. The main attention is focused on the distribution of equivalent stress values. Stresses occur in the metal structure elements with application of physiological loads. The maximum values of equivalent stresses in the structure under study at the load of 800 N (133.3 MPa) are comparable to maximum equivalent stresses in standard endoprosthesis structures, ranging from 31 to195 MPa. The maximum values do not exceed yield strength of the material, which is 350 MPa. Thus, the results of biomechanical modelling showed high operational reliability of the developed adapter with a non-standard size of the femoral component’s neck.