ArticleSpine surgery and related research2026
Sagittal Alignment-Dependent Mechanical Interference during Robotic-Assisted S2 Alar-Iliac Screw Insertion.
Article in Spine surgery and related research, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
Introduction: Although robotic-assisted spinal instrumentation enables highly accurate screw placement, mechanical feasibility constraints remain underrecognized. During sacral instrumentation, a collision between the robotic arm and the patient's body may prevent completion of S2 alar-iliac (S2AI) screw placement as planned. Alignment-related factors associated with failure of this procedure have not been clearly defined. The aim of this study was to identify spinopelvic alignment factors associated with mechanical interference during robotic-assisted S2 alar-iliac (S2AI) screw insertion. Methods: This retrospective observational study included 17 consecutive patients who underwent planned robotic-assisted S2AI screw insertion using the Cirq robotic alignment system (Brainlab) between July 2022 and January 2026. Patients were categorized into a success group (robotic guidance completed as planned) and an interference group (robotic guidance abandoned because of mechanical collision requiring conversion to a conventional technique). Supine spinopelvic parameters, including lumbar lordosis, sacral slope, pelvic tilt, and pelvic incidence, were evaluated preoperatively. Continuous variables were compared between groups using the Mann-Whitney Results: Robotic guidance was successfully completed in 13 patients (76%) and discontinued because of mechanical interference in 4 (24%). Supine lumbar lordosis was significantly greater in the interference group (median 58.5° vs. 27.6°, p=0.0008). All cases in the interference group demonstrated lumbar lordosis >50°, whereas none in the successful group exceeded this value (p<0.001). Pelvic tilt demonstrated complete separation between groups, with negative values in all interference cases and positive values in all successful cases (p=0.0008). Sacral slope was significantly higher in the interference group (p=0.0055), whereas pelvic incidence and skin-to-bone distance were not associated with interference. Conclusions: Mechanical interference during robotic-assisted S2AI screw insertion was associated with a sagittal alignment profile characterized by increased lumbar lordosis and anterior pelvic orientation. Recognition of alignment-dependent spatial constraints may improve preoperative assessment and help predict technical difficulty.
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