To investigate the biomechanical effects of sacrum-stabilized iliac traction manipulation on stress and displacement responses in the sacroiliac joint (SIJ) and iliolumbar ligament, a three-dimensional finite element model of the lumbar-pelvic complex was developed based on detailed anatomical structure. First, the articular cartilage and iliolumbar ligament were carefully reconstructed according to realistic human anatomy, with special emphasis placed on creating a solid-element representation of the ligament to accurately simulate its mechanical behavior. After model validation, simulations were performed under both physiological and manipulative loading conditions to quantitatively compare the stress, displacement, and range of motion of the SIJ and iliolumbar ligament. The results showed that under manipulative loading, the SIJ exhibited greater articular surface stress (11.057 MPa), displacement (0.209 mm), and range of motion (0.21°) than under physiological loading, although all values remained within the physiological range. The overall displacement of the iliolumbar ligament during manipulation was also found to be twice that of the joint surface. In conclusion, this study demonstrates that the therapeutic mechanism of sacrum-stabilized iliac traction manipulation primarily relies on stretching and releasing soft tissues and adjusting stress distribution between the joint surface and the iliolumbar ligament, rather than on high-amplitude joint thrust. These findings provide biomechanical support for the clinical application of this technique.
