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Introduction: Sacroiliac (SI) joint pain has become a recognized factor in low back pain. The purpose of this study was to investigate the effect of a minimally invasive surgical SI joint fusion procedure on the in vitro biomechanics of the SI joint before and after cyclic loading., Methods: SEVEN CADAVERIC SPECIMENS WERE TESTED UNDER THE FOLLOWING CONDITIONS: intact, posterior ligaments (PL) and pubic symphysis (PS) cut, treated (three implants placed), and after 5,000 cycles of flexion-extension. The range of motion (ROM) in flexion-extension, lateral bending, and axial rotation was determined with an applied 7.5 N · m moment using an optoelectronic system. Results for each ROM were compared using a repeated measures analysis of variance (ANOVA) with a Holm-Šidák post-hoc test., Results: Placement of three fusion devices decreased the flexion-extension ROM. Lateral bending and axial rotation were not significantly altered. All PL/PS cut and post-cyclic ROMs were larger than in the intact condition. The 5,000 cycles of flexion-extension did not lead to a significant increase in any ROMs., Discussion: In the current model, placement of three 7.0 mm iFuse Implants significantly decreased the flexion-extension ROM. Joint ROM was not increased by 5,000 flexion-extension cycles.