The accuracy of robot-assisted S2 alar-iliac screw placement at two different healthcare centers

BACKGROUND: Current literature on robot-assisted S2 alar-iliac (S2AI) screw placement shows favorable outcomes and screw accuracy; however, the data is limited by a few retrospective, single-surgeon studies. To the author's knowledge, this is the first multicenter study which evaluates the accuracy of robot-assisted S2AI screws. METHODS: Adult (≥18 years old) patients who underwent robot-assisted S2AI screw placement from 2017-2019 were reviewed. All surgeries used the same proprietary robotic guidance system, Mazor X (Mazor Robotics Ltd). RESULTS: A total of 65 screws were assessed in 31 patients. The mean follow-up ± standard deviation was 362±190 days (minimum was 90 days). The mean age was 61.1±11 years old, and 54.8% (n=17) of patients were female. Nearly half of the patients had a primary diagnosis of degenerative scoliosis (48.4%, n=15). Other diagnosis included pseudarthrosis (22.6%, n=7), degenerative disc disease (16.1%, n=5), and high-grade spondylolisthesis (12.9%, n=4). The mean length and diameter of screws were 84.6±6.1 mm and 8.4±0.7, respectively. The mean axial and sagittal angles were 50.0±6.3 and 24.0±10.5, respectively. The overall screw accuracy was 93.8% (n=61). There were four iliac cortex breaches (anterior =3, inferior 1) with a mean breach distance of 3.5±3.2. No statistically significant differences in screw length, diameter, axial angle, and sagittal angle were observed between screws with and without a breach. No intraoperative neurologic, vascular, or visceral complications from the S2AI screw were observed. No post-discharge wound complications, screw prominence issues, or revision of S2AI screws were observed during the study's follow-up period. CONCLUSIONS: Robot-assisted S2AI screw placement was found to be safe and accurate in this multicenter study. This is largely attributed to the versatility of the robotic guidance software that allows for detailed and precise preoperative and intraoperative planning.