Purpose: to develop and evaluate the effectiveness of a differentiated approach to knee arthroplasty in patients with gonarthrosis complicated by bone defects and instability of the ligamentous apparatus. Object and research methods. A retrospective study of the results of knee arthroplasty in 314 patients with stage IV gonarthrosis according to the Kellgren — Lawrence classification, complicated by bone defects of the femoral and tibial condyles and varying degrees of instability of the ligamentous apparatus, was conducted. A differentiated approach to selecting the type of endoprosthesis and surgical technique was applied depending on the size of the defect and the state of the ligamentous apparatus. The results. It has been established that in case of condylar defects <5 mm, bone cement replacement with endoprosthesis implantation without preservation of the posterior cruciate ligament is effective. For defects >5 mm, it is optimal to use augments with an endoprosthesis without preserving the posterior cruciate ligament. In cases of combined defects and partial failure of collateral ligaments, the use of endoprostheses of the LCCK type proved to be effective. In the case of significant damage to the ligamentous apparatus, the best results were shown by the use of integral endoprostheses of the Hinge type. Conclusion. The proposed differentiated approach to knee arthroplasty allows to optimize the surgical treatment of patients with gonarthrosis complicated by bone defects and instability, providing better functional results and reducing the risk of complications. Individualization of the choice of endoprosthesis type and surgical technique is a key factor in the successful treatment of complex forms of gonarthrosis.