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Radio-anatomical study of anterior–posterior placement sacroiliac screw channel



The outlet of the classic sacroiliac screw (SIS) cannot be precisely controlled by aiming devices, which may lead to malpositioned implants and neurovascular and visceral injury. This study aimed to radio-anatomically measure the parameters of the channel for anterior–posterior placement SIS (AP-SIS), which can be placed percutaneously with an aiming device.


Pelvic CT scan data of 80 healthy adults (40 males and 40 females) with an average age of 45 years (range 20–70 years) were collected. The length (L), width (W), height (H), cortical bone spacing (M), camber angle (E), anteversion angle (F), cross-sectional safety angle (P) and sagittal safety angle (Q) of the channel were measured by CT or Mimics software.


The L, W, H, M, E, F, P and Q measures of S1 were 109.2 ± 8.0 mm, 18.5 ± 1.9 mm, 21.7 ± 1.7 mm, 8.1 ± 0.4 mm, 44.2 ± 3.2°, 42.4 ± 3.6°, 16.8 ± 1.1°, and 19.4 ± 2.0°, respectively, for S1, and 113.5 ± 9.4 mm, 18.2 ± 1.5 mm, 21.7 ± 1.7 mm, 7.7 ± 0.4 mm, 44.7 ± 3.2°, 31.2 ± 2.7°, 13.8 ± 1.0° and 15.4 ± 1.4°, respectively, for S2. Of the L measures, the intra-iliac segment was slightly longer than the intra-sacral segment. All parameters showed significant sex-related differences (p < 0.05).


The AP-SIS channels of S1-2 have sufficient width and length to accommodate a cancellous screw with a Φ 7.0–8.0 mm and a length 90–130 mm. The intra-iliac segment is a long channel screw with better mechanical properties over classic SIS.

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Sacroiliac screw


Sacral–alar–iliac screw


Anterior–posterior placement sacroiliac screw


First sacral vertebra


Second sacral vertebra

L :

Length of the channel

W :

Width of the channel

H :

Height of the channel

E :

Camber angle

F :

Anteversion angle

P :

Cross-sectional safety angle

Q :

Sagittal safety angle

M :

Cortical bone spacing


Anterior inferior iliac spine


Iliac cortical density


Intraclass correlation coefficient


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The authors would like to express their gratitude to EditSprings ( for the expert linguistic services provided.


This study was supported by Project of Academician Qiu Guixing workstation of Wuxi No. 9 People's Hospital (No. JY2020-02), the Top Medical Expert Team of “Taihu Talent Program” in Wuxi (2020) (TTP-TMET2020-09). The beneficiaries of the funds were Yunhong Ma and Qudong Yin.

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Authors and Affiliations



WCB, YQD and GSJ reviewed the literature, collected, and analyzed the data and wrote the manuscript. MYH, LY and WCB analyzed the data, final reviewed the literature and were responsible for the project and manuscript.

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Correspondence to Yunhong Ma or Qudong Yin.

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The authors declare no competing interests.

Ethics approval and consent to participate

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional standards. Ethics committee approval was obtained for this retrospective study (No. KT2021012; registration date: May 2021, retrospective registration), which abandoned the written consent of patients.

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Wang, T., Wei, C., Gu, S. et al. Radio-anatomical study of anterior–posterior placement sacroiliac screw channel. Eur Spine J (2022).

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  • Sacroiliac screw
  • S2AI
  • Radiology
  • Anterior–posterior placement
  • Aiming device