Sacroiliac joint fixation with a posterior intra-articular implant versus a posterolateral transiliac implant: A biomechanical comparison

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Background Along with the growing recognition of sacroiliac joint dysfunction as a contributor to chronic low back pain has come the increase in the utilization of sacroiliac fusion devices. Relative to the various surgical approaches for sacroiliac joint fusion, the posterior intra-articular approach has been described as a potentially less invasive approach that has less proximity to critical neurovascular structures. Methods In this controlled cadaveric study, posterior and posterolateral sacroiliac fixation implants are compared, characterizing each implant's joint stabilization, resistance to fatigue loading, implantation geometry, and positional safety. Pelves were subjected to isolated flexion/extension, lateral bending, axial rotation, and axial compression loads in intact, destabilized, fixed, and post-fatigue conditions. Reductions in motion were computed with optical marker tracking. Positional safety was assessed through radiographic measurements from each implant to salient anatomic landmarks. Results Compared to the posterolateral implant, the novel posterior implant provides improved flexion/extension stability both after fixation (33% versus 0% motion reduction, p < 0.01) and after fatigue loading (25% reduction versus 1% increase, p < 0.05). The posterior implant reduces device migration after fatigue loading (0.1 mm versus 0.7 mm, p < 0.05), removes less bone during placement (955 mm 3 versus 3,248 mm 3 , p < 0.001), and is placed further from both the sacral foramina (14.1mm versus 4.6 mm, p < 0.01) and the anterior border of the joint (21.3 mm versus 7 mm, p < 0.05). No statistically significant differences were found for stability under other loading configurations, surface area available for fusion, or joint width changes. Conclusions These cadaveric findings suggest biomechanical stability and positional safety advantages for the posterior device. Additional data on patient outcomes, fusion rates, and intraoperative safety is needed to assess clinical performance.