Manipulations of oblique pulling affect sacroiliac joint displacements and ligament strains: a finite element analysis

Abstract Background Clinical studies have found that Manipulation of oblique pulling (MOP) has a good clinical effect on sacroiliac joint (SIJ) pain without specific causes. However, there is no uniform standard for MOP at present. The effects of MOPs with different force points and directions on SIJs are not clear. The purpose of this study was to investigate the effects of four MOPs on the stresses and displacements of the normal SIJ and the strains of the surrounding ligaments. Methods A three-dimensional finite element model of the pelvis was established. Four MOPs were simulated. The stresses and displacements of the SIJ and the strains of the surrounding ligaments were analyzed under four MOPs. Results MOP-F2 caused the highest stress on the pelvis, at 85.0 MPa, while MOP-F3 caused the lowest stress on the pelvis, at 52.6 MPa. MOP-F3 produced the highest stress on the left SIJ, at 6.6 MPa, while MOP-F1 produced the lowest stress on the left SIJ, at 5.6 MPa. The four MOPs mainly produced anterior-posterior displacement of SIJ. The maximum value was 1.21 mm, produced by MOP-F2, while the minimal value was 0.96 mm, produced by MOP-F3. The four MOPs could all cause different degrees of ligament strain around the SIJ, and MOP-F2 produced the greatest ligament strain. Conclusions The four MOPs all produced small displacements of the SIJ and different degrees of ligament strain. MOP-F2 produced the largest displacement of SIJ and the greatest ligament strain, which could provide a certain reference for physiotherapists.