The technique of S2-alar-iliac screw fixation: a literature review

The distal fixation in thoracolumbar deformity surgery can be challenging for spine surgeons. When isolated S1-pedicle screws are utilized as the sole distal fixation in long thoracolumbar posterior constructs, there is a high rate of failure, due to loosening, breakage, and pseudarthrosis. Unfortunately, with iliac screw fixation the entry point at the posterior superior iliac spine requires considerable soft tissue dissection and may potentially increase the likelihood of wound complications. S2-alar-iliac (S2AI) screw fixation technique was developed recently to provide increased fixation with a lower profile screw and rod construct. These screws can be inserted with percutaneous or free hand techniques. This fixation also has comparable biomechanical properties to the S1 iliac screw. This technique may provide advantages such as decreased rates of reoperation, surgical site infection, wound dehiscence and symptomatic screw prominence as compared to traditional iliac screw fixation. The purpose of this manuscript is to review the S2AI screw fixation literature including anatomy, technique, biomechanics, and clinical outcomes.