Biomechanical Analysis of the Joint and Muscle Forces of the Lower Extremities in Walking of Rheumatoid Arthritis Patient

Summary. Rheumatoid arthritis (RA) is an immunomodulated, chronic inflammatory disease, accompanied by the proliferation of the inflamed synovium and destruction of the articular cartilage, which leads to the formation of contracture of lower extremities joints and disability. Understanding the values of biomechanical loads on the articular surfaces with contracture of the joints of the lower extremities in patients with RA and the muscle forces (MF) participation in this process with the formation of adaptation and compensation mechanisms can contribute to the development of new views and approaches to the tactics of therapeutic measures specific to each stage of the disease. Objective: to analyze the behavior of the musculoskeletal system of an RA patient in his walking pattern by calculating the forces acting in the main muscle groups and joints of the lower extremities. Materials and Methods. Initial data were obtained from the examination of a female patient K., who was diagnosed with stage 2 phase 3 RA with a predominant lesion of the hip and knee joints and severe pain in the left hip joint. A video system of 6 cameras, reflective markers and a force platform were used for motion capture of the walking. A simulation musculoskeletal model of the gait of the RA patient using the AnyBody Modeling System 6.0 software (Denmark) was created. Joint reaction forces (JRF) and MF were calculated. Results. Normal mode of loading of the lower extremities was altered to compensate for structural disorders in joints of RA patients. The peaks of vertical component of the ground reaction force (GRF) are lower compared to the normal population; the gait is static and asymmetric, sparing. MF increase in m. gluteus (maximus, medius, minimus) with increasing amplitude of movements in the frontal plane. JRF of both hips increase in all planes. Conclusions. Walking of RA patients with limitation of active extensions in the hip and knee joints occurs due to an increase in the amplitude of the frontal plane compensatory movements. Postural muscle imbalance increases the m. gluteus, m. biceps femoris, m. semitendinosus and m. semimembranosus MF. Other lower extremities muscles decrease their MF. The MF redistribution is compensatory and aimed to keep the RA patient in the upright position and optimize the biomechanics of walking due to less painful movements. Biomechanical overloading of the hip and knee articular surfaces can serve as a factor in maintaining the inflammatory response, the development of degenerative processes, or the further progression of arthrosis and stiffness of the joints of the lower extremities in this category of patients.