Biomechanical Analysis of Stress–Strain Distribution in the Lumbar Spine–Sacrum–Pelvis System with Emphasis on Sacroiliac Joint Dysfunction

Background: Chronic lumbopelvic pain is often linked to sacroiliac joint dysfunction, where the joint’s complex structure and biomechanics complicate diagnosis and treatment. Variability in load distribution and ligament stabilization within the pelvic ring further contributes to challenges in managing this condition. This study aims to develop a finite element model of the “lumbar spine–sacrum–pelvis” system to analyze the effects of lumbar lordosis, pelvic tilt, and asymmetrical articular gaps on stress and strain in the sacroiliac joint. Methods: A three-dimensional model was constructed using CT and MRI data, including key stabilizing ligaments. Sacral slope angles of 30°, 60°, and 85° were used to simulate varying lordosis, while pelvic tilt was introduced through a 6° lateral rotation. Results: The analysis revealed that sacral slope, ligament integrity, and joint symmetry significantly influence stress distribution. Hyperlordosis led to critical stress levels in interosseous and iliolumbar ligaments, exceeding failure thresholds. Asymmetrical gaps and pelvic tilt further altered the sacral rotation axis, increasing stress on sacroiliac joint ligaments. Conclusions: These findings highlight the importance of maintaining sacroiliac joint symmetry and lumbar–pelvic alignment to minimize stress on stabilizing ligaments, suggesting that treatment should focus on restoring alignment and joint symmetry.