A Finite Element Analysis of Sacroiliac Joint Ligaments in Response to Different Loading Conditions

Study Design. A finite element analysis of the sacroiliac joint (SIJ) and its associated ligaments utilizing a three-dimensional model constructed from computed tomography scans. Objective. To characterize the sacroiliac ligament strains in response to flexion, extension, and axial rotation loads and quantify the changes in SIJ stress and angular displacement in response to changes in ligament stiffness. Summary of Background Data. The SIJ may be a major contributor to low back pain in up to 13% to 30% of patients. States of ligament laxity are often associated with hypermobility and possibly pain of SIJ origin. The mechanism by which the SIJ generates pain is both controversial and poorly understood. Methods. A finite element model of the human pelvis, SIJs, and sacroiliac ligaments was constructed from computed tomography scans. Ligament stiffnesses were altered and the SIJ stresses were compared with the original case. For simulated flexion, extension, and axial rotation scenarios, sacroiliac ligament strains were characterized and compared. Results. Sacroiliac joint stress and angular motion increases as ligament stiffness decreases. Periarticular intraligamentous strains vary depending on the magnitude and direction of the applied loads. Maximum ligamentous strains occur at the interosseous sacroiliac ligament. Conclusion. The sacroiliac ligaments function to constrain the SIJ and decrease stress across the SIJ for different load scenarios. Decreasing sacroiliac ligament stiffness leads to both increased joint motion and stress.