1.Insufficient evaluation of S2 alar iliac screw malposition with the intraoperative inlet view: utility of the obturator inlet and iliac oblique views
Shun OKUWAKI ; Toru FUNAYAMA ; Yohei YANAGISAWA ; Takahiro SUNAMI ; Takane NAKAGAWA ; Yosuke OGATA ; Kotaro SAKASHITA ; Hisanori GAMADA ; Kousei MIURA ; Hiroshi NOGUCHI ; Hiroshi TAKAHASHI ; Masao KODA
Asian Spine Journal 2026;20(2):302-312
Methods:
We analyzed data from 101 patients who underwent spinopelvic surgery involving 202 S2AI screws. Postoperative computed tomography (CT) images were reviewed to identify screw deviations. The reconstructed fluoroscopic views from CT, including the inlet, OI, and IO views, were assessed for their effectiveness in detecting deviations. An experimental study using pelvic bone models simulated scenarios where deviations were undetectable in the inlet view but visible in the OI view.
Results:
Screw deviations were identified in 12 cases (11.9%) and 13 screws (6.4%), including six screws (3.0%) with anterior deviations and seven screws (3.5%) with posterior deviations. The accurate inlet view detected anterior deviations in three of the five cases analyzed with reconstructed images. However, two cases of anterior deviation were missed due to an insufficient inlet view caused by a 30° caudal tilting angle. In contrast, the OI view successfully identified all cases of both anterior and posterior deviations. In particular, deviations above the arcuate line of the pelvic brim were not detectable in the inlet view.
Conclusions
The inlet view alone is inadequate for detecting anterior deviations, especially those located above the arcuate line of the pelvis. The OI and IO views demonstrated greater effectiveness in identifying deviations, thereby enhancing the accuracy and safety of S2AI screw placement.
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