Quantitative study on the biomechanical mechanism of sacroiliac joint subluxation: A finite element study

The biomechanical mechanism of sacroiliac joint pain caused by sacroiliac joint subluxation is still unclear. And the purpose of this study is to elucidate the mechanism. In the present study, a finite element model of female lumbar spine-pelvis-femur was established. To simulate the sacroiliac joint subluxation quantitatively, the left ilium was shifted +/- 1, +/- 2, and +/- 3 mm along each axis, respectively. The stress and strain of articular surfaces and ligaments between the sacroiliac joint subluxation model and the normal model were compared. When the left ilium shifted along the positive direction of the X/Y/Z axis, the stress on most articular surfaces of the sacroiliac joint increased, of which the stress on the iliac surface of the right sacroiliac joint increased most obviously. The stress and strain of the ligaments increased most obviously when the left ilium shifted along the Y-axis, of which the left sacrospinous ligament increased the most, followed by the right sacrospinous ligament and right long posterior sacroiliac ligament. While the left long posterior sacroiliac ligament decreased the most, followed by the left short posterior sacroiliac ligament. The present study suggests that when the sacroiliac joint subluxation happens, even a slight shift, different biomechanical changes of different ligaments around the sacroiliac joint will happen. This may lead to an abnormal proprioceptive sensation of the ligaments, resulting in stress imbalance of the sacroiliac joint, and finally resulting in sacroiliac joint pain.