Methods for complex assessment of operational life of the functional material in hip replacement. Report 1

The papers presents an approach to an integrated evaluation of the operational durability of the “bone - endoprosthesis” system during hip replacement taking into account a patient's personal parameters (age, joint geometry, individual functional loads, mechanical and adaptive properties of bone tissue). A “functional material” is understood as not just a material but a certain structure which includes several materials (substructures) that interact with each other and provide a given set of operational characteristics. The “bone - implant” structure is an example of such a “functional material”. The solution of the problem related to a complex evaluation under conditions of uncertainty associated with a patient's age is accomplished by constructing a generalized optimality criterion that is represented by a set of particular criteria of a different importance (the degree of adaptive osteoporosis development and the area of the bone bed traumatization). The clinical significance of the selected biomechanical criteria for patients of different age groups is estimated using the importance scale from 0 to 10. Individual numerical values of biomechanical criteria are calculated using the spatial anisotropic linear elastic mathematical model of the hip joint. To carry out a comparative analysis of the operational durability of different types of endoprostheses, three different implant designs have been chosen with cement and cementless fixation method. Clinical recommendations to choosing the type of endoprosthesis depending on a patient's age are also evaluated using the scale from 0 to 10. The operational durability of a particular type of endoprosthesis is regarded as a special fuzzy set of values of all particular criteria with corresponding values of their importance for different age groups. The introduction of a special function called the ranking index enabled the solution of the problem of a multi - objective choice of the endoprosthesis design in conditions of uncertainty associated with a patient's age. The proposed approach allows choosing the best implant design for both primary and revision arthroplasty taking into account the clinical and biomechanical parameters of a patient. A demonstration example of solving the problem of multi - objective selection of the best endoprosthesis design taking into account a patient's age will be presented in Report 2.