Biomechanical Evaluation of the Effect of MIS and COS Surgical Techniques on Patients with Spondylolisthesis using a Musculoskeletal Model

Background: The biomechanical impacts of Conventional Open Surgery (COS) versus Minimally Invasive Surgery (MIS) fusion techniques on adjacent segments and their potential role in developing Adjacent Segment Disease (ASD) remain uncertain for spondylolisthesis. Objective: This study aimed to investigate the impact of MIS and COS fusion surgeries on adjacent spinal segments for spondylolisthesis, through on muscle injury and developing ASD. Material and Methods: This prospective and non-randomized controls study used a validated musculoskeletal model to compare the biomechanical effects of COS and MIS L₄ /L₅ fusion surgery on patients with spondylolisthesis. The model incorporated kinematic data from 30 patients who underwent each surgery. A sitting task was simulated to model post-operative muscle atrophy, and the analysis focused on changes in biomechanics of adjacent spinal segments. Results: Lumbar flexion was significantly greater (201%) in MIS vs. COS, despite similar pelvic tilt. Consequently, Lumbopelvic Rhythm (LPR) also increased in MIS (133%). Both techniques altered inter-segmental moments. While inter-joint load was higher in COS, only the lower joint’s compressive load was significantly greater (67%). Additionally, MIS required lower overall muscle force with reduced loads and passive moment on spinal joints compared to COS. Conclusion: This study demonstrates that MIS fusion preserves physiological LPR better than COS. MIS maintains normal spinal curvature and maintains lumbar lordosis. While open surgery can lead to abnormal curvature and increased muscle forces to compensate for spinal stability. The study emphasizes the importance of paraspinal muscles in influencing spinal load distribution during MIS compare to COS.