Introduction: To compare clinical and radiographic outcomes between the S2-alar-iliac (S2AI) and the iliac screw (IS) techniques in the adult population and clarify the clinical strength of S2AI screws.S2AI screws have been described as an alternative method for lumbosacropelvic fixation in place of ISs. The S2AI technique has several advantages with lower prominence, increased ability to directly connect to proximal instrumentation, less extensive dissection of tissue, and enhanced biomechanical strength over the IS technique. However, the clinical significance of these advantages remains unclear.

Methods: A single-center retrospective review of patients who underwent lumbosacropelvic fixation yielded 25 IS group patients and 65 S2AI group patients. Baseline demographic information, postoperative complications, pain and functional outcomes, and screw-related outcomes were collected.

Results: The S2AI group had lower rates of reoperation (8.8% versus 48.0%, p < 0.001), surgical site infection (SSI) (1.5% versus 44.0%, p < 0.001), wound dehiscence (1.5% versus 36.0%, p < 0.001), and symptomatic screw prominence (0.0% versus 12.0%, p = 0.02) than the IS group, while rates of L5-S1 pseudarthrosis, proximal junctional failure, and sacroiliac joint pain were similar in both groups. Statistically significant pain relief and functional recovery were achieved in both groups without any significant intergroup differences. On multivariate analyses, age (odds ratio (OR) = 0.91, p = 0.004) and S2AI instrumentation (OR = 0.08, p < 0.001) were protective of reoperation, whereas diabetes mellitus (OR = 10.9, p =0.03) and preoperative diagnosis of tumor (OR = 12.3, p = 0.04) were associated with SSI, and S2AI instrumentation (OR = 0.09, p < 0.001) was protective of SSI.

Conclusions: The use of the S2AI technique over the IS technique was an independent predictor of preventing reoperation and SSI, while achieving similar clinical and functional outcomes.

Patient Care: It was demonstrated that the S2AI technique was advantageous in many aspects such as lower rates of reoperation, SSI, wound dehiscence, and screw prominence. Further prospective studies are warranted to determine what kind of patient populations benefit most from it.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the advantages of S2AI screws over ISs, 2) Discuss, in small groups,how these results can be translated into clinical practice

References: O’Brien Joseph R., Yu Warren D., Bhatnagar Rishi., et al. An anatomic study of the S2 iliac technique for lumbopelvic screw placement. Spine (Phila Pa 1976) 2009;34(12):E439–42. Doi: 10.1097/BRS.0b013e3181a4e3e4. Guler Umit Ozgur., Cetin Engin., Yaman Onur., et al. Sacropelvic fixation in adult spinal deformity (ASD); a very high rate of mechanical failure. Eur Spine J 2015;24(5):1085–91. Doi: 10.1007/s00586-014-3615-1. Martin Christopher T., Witham Timothy F., Kebaish Khaled M. Sacropelvic Fixation. Spine (Phila Pa 1976) 2011;36(9):E618–21. Doi: 10.1097/BRS.0b013e3181f79aba.