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Purpose <p>To evaluate the geometric feasibility of using the anterior inferior iliac spine (AIIS) as an anatomical reference for S2-alar-iliac (S2AI) screw placement.</p> Methods <p>Computed tomography scans of 80 Chinese adults with normal pelvic anatomy were analyzed. AIIS-referenced S2AI trajectories were compared with CT-defined optimal S2AI trajectories based on geometric parameters. Measurements included maximal screw length, transverse and sagittal angulation, narrowest iliac width, and angular margins. Two commonly used S2AI entry points were evaluated: entry point A, located 1&#xa0;mm inferior and lateral to the S1 dorsal foramen, and entry point B, located at the midpoint between the S1 and S2 dorsal foramina at the lateral sacral crest.</p> Results <p>AIIS-referenced S2AI trajectories showed small angular deviations from the CT-defined optimal trajectories, with an average difference of approximately 2° in the sagittal plane. No significant difference was observed in maximal screw length between the two trajectories (<i>P</i> &gt; 0.05), while the optimal trajectory demonstrated a slightly greater narrowest iliac width (<i>P</i> &lt; 0.05). For AIIS-referenced trajectories, the narrowest iliac width did not differ significantly between the two entry points (<i>P</i> &gt; 0.05). Entry point B showed a longer maximal screw length (<i>P</i> &lt; 0.05) and larger angular margins in the coronal plane for both 60-mm and 80-mm simulated screws (<i>P</i> &lt; 0.05). In the sagittal plane, both entry points demonstrated comparable angular ranges, with entry point A showing a slightly larger caudal angular margin (<i>P</i> &lt; 0.05).</p> Conclusion <p>In individuals with normal pelvic anatomy, AIIS-referenced S2AI trajectories demonstrate small geometric differences compared with optimal trajectories and allow accommodation of standard-length and diameter screws within an acceptable intraosseous corridor. Minor geometric differences were observed between the two commonly used entry points. These findings support the use of the AIIS as a practical anatomical reference for planning S2AI screw trajectories.</p>

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Anterior inferior iliac spine as an anatomical reference for S2-alar-iliac screw placement: a three-dimensional computed tomography-based study

  • 期刊论文

  • 发表日期：

    2026年4月9日

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  • Pan Yi Yang,
  • Dao Xi Wang,
  • Xue Yang Tang,
  • Zhi Xia Chen,
  • Li Zou,
  • Lei Yang

摘要

Purpose

To evaluate the geometric feasibility of using the anterior inferior iliac spine (AIIS) as an anatomical reference for S2-alar-iliac (S2AI) screw placement.

Methods

Computed tomography scans of 80 Chinese adults with normal pelvic anatomy were analyzed. AIIS-referenced S2AI trajectories were compared with CT-defined optimal S2AI trajectories based on geometric parameters. Measurements included maximal screw length, transverse and sagittal angulation, narrowest iliac width, and angular margins. Two commonly used S2AI entry points were evaluated: entry point A, located 1 mm inferior and lateral to the S1 dorsal foramen, and entry point B, located at the midpoint between the S1 and S2 dorsal foramina at the lateral sacral crest.

Results

AIIS-referenced S2AI trajectories showed small angular deviations from the CT-defined optimal trajectories, with an average difference of approximately 2° in the sagittal plane. No significant difference was observed in maximal screw length between the two trajectories (P > 0.05), while the optimal trajectory demonstrated a slightly greater narrowest iliac width (P < 0.05). For AIIS-referenced trajectories, the narrowest iliac width did not differ significantly between the two entry points (P > 0.05). Entry point B showed a longer maximal screw length (P < 0.05) and larger angular margins in the coronal plane for both 60-mm and 80-mm simulated screws (P < 0.05). In the sagittal plane, both entry points demonstrated comparable angular ranges, with entry point A showing a slightly larger caudal angular margin (P < 0.05).

Conclusion

In individuals with normal pelvic anatomy, AIIS-referenced S2AI trajectories demonstrate small geometric differences compared with optimal trajectories and allow accommodation of standard-length and diameter screws within an acceptable intraosseous corridor. Minor geometric differences were observed between the two commonly used entry points. These findings support the use of the AIIS as a practical anatomical reference for planning S2AI screw trajectories.