STUDY OF THE LIV VERTEBRAL BODY LOAD DURING DYNAMIC SIMULATION OF MOVEMENTS IN THE LUMBAR SPINE USING MUSCULOSKELETAL MODELS AFTER POSTERIOR BISEGMENTAL SPINE FUSION PERFORMANCE

One of the risk factors for complications in the spinal motion segments of the thoracic and lumbar regions, as well as in the adjacent segments with spinal fusion ones, is changes in the sagittal vertebral-pelvic balance. Purpose. To determine the effect of muscle changes that occur during the performance of two-segment LIV–SI spinal fusion on the load of adjacent motion segments. Material and methods. The spinal fusion of two spinal motion segments of the lumbar spine was simulated at the LIV–LV and LV–SI levels at different angles of segment fixation in the OpenSim programme. Five models were analysed: 1 (basic) — without changes; 2 — changes in the points of attachment and muscle strength; 3 — normo-lordotic fixation; 4 — hypolordotic; 5 —hyperlordotic. The load on the zone of interest was measured as the magnitude of the projection of the force vector depending on the angle of inclination of the torso as a percentage of the body weight. Results. Simulation of the above configurations of the instrumental spinal fusion (intact, normo-lordotic, hyperlordotic, hypolordotic positions due to a change in the angle of the LIV–SI spinal fusion) showed that the load force of the adjacent segments when bent forward depended on the angle of the instrumental spinal fusion performed. Conclusions. As a result of study of the kinematic model of the lumbar spine using bisegmental spinal fusion of LIV–SI, it was proved that the load force of the adjacent segments when bent forward depended on the angle of the instrumental spinal fusion performed. It was determined that the upper adjacent vertebra of the fixation zone had a relatively insignificant increase in load in the case of fixation in the hyperlordotic position; in the hypolordotic position, the load on the upper segment led to an increase in loads on the upper adjacent segment, and in the hypolordic position, it led to a slight decrease compared to the normo-lordotic fixation. According to the results of the study, minimal muscle damage is expected during the surgical intervention, so the reliability of the model is closer to minimally invasive surgery. The developed kinematic models can be useful in the planning of the transpedicular fixation surgery to prevent complications.