Introduction: Rigid spinopelvic fixation is necessary to anchor and maintain the stability of long fusion constructs in spinal deformity surgery, with additional applications in spinal trauma, tumor, infection, and degenerative conditions. Current techniques to enhance spinopelvic stabilization include multiple rod constructs, bicortical S1 pedicle screws, traditional iliac screws, S2 alar-iliac (S2AI) screws, anterior interbody grafts, and combinations thereof.
Distal failure, including screw fracture, screw head/shaft disengagement, pullout, and loosening continue to pose a difficult challenge. Supplemental or alternative pelvic fixation may become necessary in cases of poor bone quality, trauma, or anatomic anomalies which limit the ability to place standard sacral or pelvic fixation.
Methods: Two fresh-frozen human cadavers were surgically dissected exposing approximately L3-S4. BrainLab AIRO CT navigation was used to plan and insert unilateral Depuy-Synthes Expedium S1AI and S2AI screws. Under CT navigation, a navigated gearshift was advanced from the starting point through the sacro-iliac joint, aiming just superior to the greater trochanter. Approximately 25° of caudal angulation in the sagittal plane and 35° of horizontal angulation in the axial plane was required. S2AI screws were placed using CT navigation using previously described techniques. Screw position was confirmed with post-placement CT. The screws were subsequently removed, and repeat CT was obtained.
Results: Unilateral S1AI and S2AI screws were successfully placed. The starting point of the S1AI screw is located at the inferior-lateral L5-S1 facet joint, identical to the S1 pedicle starting point. There were no cortical breaches. Excellent insertional torque and screw purchase was noted. 80-100 mm length and 10 mm diameter screws were placed. The screws were in-line with each other allowing for easy rod seating.
Conclusions: S1AI screws can be safely placed and serve as alternate means of distal fixation. Future work elucidating their biomechanical profile and clinical application is in progress.
Patient Care: A novel technique of sacral or spinopelvic fixation is introduced. S1AI screws can replace sacral pedicle screws, and/or supplement S2AI screws.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the indications for standard and supplemental pelvic fixation and 2) Understand the S1AI screw technique and trajectory.and