Pelvic fixation with quad rod technique using S1.5 and S2 Alar-Iliac screws: a technical note and case series

Introduction: Pelvic fixation strategies in long-segment adult spinal deformity (ASD) surgery continue to evolve to optimize construct durability and clinical outcomes. Here we aim to 1) provide a detailed description of a surgical technique utilizing bilateral S1.5AI pelvic screws in conjunction with traditional S2AI screws to establish robust multipoint pelvic fixation and 2) evaluate outcomes in a clinical case series.

Methods: A consecutive series of patients was retrospectively identified at a single institution from 2018-2024. Inclusion criteria: 1) Patients surgically treated for ASD, 2) Multipoint pelvic fixation using bilateral S1.5AI and S2AI screws placed with standardized technique including quad rod placement. 3) Adequate clinical and radiographic follow-up. Detailed surgical technique description and retrospective case series are provided.

Results: 18 patients met inclusion criteria. Average age was 61.2 years, 22.2% males, average BMI was 29.2±8.5. Four patients (22.2%) had preoperative weakness. 14 patients (77.8%) had upper-instrumented vertebrae within the thoracic spine; with an mean construct length of 9.3. Mean EBL was 1023.5cc and the mean operating time was 7.15±1.6 hrs. S1.5AI screws were placed bilaterally with an entry point within the lateral aspect of the S1 foramen. Traditional S2AI screws were placed either along the line tangent to the medial board of the S1 and S2 foramen or more medial and served as the attachment point for a medial accessory rod. Three iliac wing fractures were identified on postoperative CT (16.7%); all were asymptomatic and did not require intervention. There were no neurological changes, readmissions, or reoperations related to this technique.

Conclusion : We present a technical note and case series describing a method for multipoint pelvic fixation using bilateral S1.5AI screws combined with traditional S2AI screws. Our data shows a low risk profile for placement and low peri-operative complication rates. This method is an effective means of establishing robust pelvic fixation with high safety profile.