Robotic-guided sacro-pelvic fixation using S2 alar-iliac screws: feasibility and accuracy

To review our experience with robotic guided S2-alar iliac (S2AI) screw placement. We retrospectively reviewed patients who underwent S2AI fixation with robotic guidance. Screw placement and deviation from the preoperative plan were assessed by fusing preoperative CT (with the planned S2AI screws) to postoperative CT. The software's measurement tool was used to compare the planned vs. actual screw placements in axial and lateral views, at entry point to the S2 pedicle and at a 30 mm depth at the screws' mid-shaft, in a resolution of 0.1 mm. Medical charts were reviewed for technical issues and intra-operative complications. 35 S2AI screws were reviewed in 18 patients. The patients' mean age was 60 years. No intra-operative complications that related to the placement of S2AI screws were reported and robotic guidance was successful in all 35 screws. Post-operative CT scans showed that all trajectories were accurate. No violations of the iliac cortex or breaches of the anterior sacrum were noted. At the entry point, the screw deviated from the pre-operative plan by 3.0 +/- 2.2 mm in the axial plane and 1.8 +/- 1.6 mm in the lateral plane. At 30 mm depth, the screw deviated from the pre-operative plan by 2.1 +/- 1.3 mm in the axial plane and 1.2 +/- 1.1 mm in the lateral plane. Robotic guided S2AI screw placement is feasible and accurate. No screw malpositions or complications that related to the placement of S2AI screws occurred in this series. Larger studies are needed to assess the long-term clinical outcomes of robotic guided sacral-pelvic fixation.