An anatomic study of the S2 iliac technique for lumbopelvic screw placement

STUDY DESIGN. An anatomic study conducted on cadaveric specimens. OBJECTIVES. The objectives of the study were (1) to determine course of S2 lumbopelvic screws with reference to the articular cartilage of the sacroiliac joint, (2) to determine the length and trajectory of screws placed using anatomic placement techniques, and (3) to determine vital structures at risk using this technique. SUMMARY OF BACKGROUND DATA. Multiple techniques exist for fixation distal to S1 including alar screws, iliac post bolts, and transiliac rods. Distal fixation is crucial in adult deformity surgery when fusion to the sacrum is indicated. METHODS. Five female and 5 male cadaveric specimens were instrumented with S1 promontory screws and S2 iliac lumbopelvic screws. The specimens then underwent computed tomography scanning to determine structures at risk, cortical violations, and characteristics of screws placed. The sacroiliac joints were opened to examine articular cartilage penetration. RESULTS. Articular violation occurred in 60% of screws placed. Average length was 84 mm. No vital structures were at risk from screw placement. No intrapelvic cortical violations occurred. CONCLUSION. S2 iliac technique is a potential option for distal fixation in spine surgery. Biomechanical and clinical data are required to fully evaluate the potential of this technique.