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Background. Rheumatoid arthritis (RA) is an immunomodulatory, chronic inflammatory disease accompanied by the proliferation and articular cartilage destruction that cause disability. Biomechanical factors in RA can play an important role in the onset and progress of the joint degenerative processes, secondary to the inflammation process. The biomechanical factors in RA can play an essential role in the start and progress of the degenerative processes within the joint that are secondary to the inflammatory process. Materials and methods. A solid simulation 3D-model of the knee joint was created that contained both tibia and fibula, the femur bone, femoral condyle cartilage and tibial plateau cartilage, menisci. It was done for further analytical calculations and finite element modeling calculations. Analytical calculations are based on the data of previous studies of quantitative evaluation of the knee joint contracture (compliance of contracture to the external corrective action) and on calculations data of the joint forces that manifest in ambulation of the patient with RA. Results. The created simulation computer 3D-model of a knee joint with its flexion contracture at late stages of RA shows that the forced passive flexion in the knee joint to 6°, the load on the condyles of the tibial plateau increased by 12.8 %, and as a result of forced passive flexion in the knee joint to 3°, the load on the condyles of the tibial plateau increased by 95.2 %, which is critical and may cause degradation of the bone tissue in the contact area. Conclusions. Increase of load on the lateral areas of the tibial plateau and, correspondingly, the tensions on the contact areas of the femur bone condyles with the tibial plateau, may contribute to the progress of the clinical picture of RA with the increase of arthrofibrosis and osteoarthritis events, particularly in the lateral areas of the knee joint. [ABSTRACT FROM AUTHOR]