PMC7276580_01
Case 1. (a) Radiograph before surgery. White arrow indicates the irregularly larger round foramen. (b) 3D computed tomography (CT) image of after surgery. (c) CT after surgery showed that plate and screws were closed to ventral sacrum foramen. Black circle indicates the right irregularly larger round foramen induced by transitional vertebrae.
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F1
However, in this surgery, the nerve root ran from the irregularly larger round foramen to the lateral side more than usual, and therefore, the nerve root was exposed (Fig. 1).
PMC7276580_02
Case 2. (a) Pelvic outlet view. (b) Pelvic inlet view. The most cranial inserted screw (white arrow) did not penetrate the sacrum anterior margin. (c) Computed tomography image after surgery showed that the most cranial screw (white arrow) was inserted toward the anterior portion of sacrum and attached the nerve root. (d and e) Revision surgery. The most cranial screw was removed and inserted the screw again (white arrow) at slightly inferior posterior area.
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F2
Immediately, the screw was removed and reinserted in a slightly posterior area (Fig. 2).
The demography of intraoperative C-arm images reconstructed by 3D computed tomography images. Even if C-arm tube angled more caudally (from inlet view 1 to inlet view 2), the anterior margin of the small cranial portion of the sacrum (a dotted line) cannot be shown clearly due to overhanging the anterior margin of caudal portion of the sacrum (black line).
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F3
In this case, the anterior margin of the small cranial portion of the sacrum was not shown clearly by inlet view during surgery due to overhanging the anterior margin of the caudal portion of the sacrum (Fig. 3).
PMC7276580_03
Case 3. (a) Computed tomography coronal image: Dysplastic transverse process (white circle)and left small sacroiliac articular space (black circle).(b) The angulation of two S2 alar-iliac screws was limited and only one cylinder cage was inserted due to his small sacroiliac articular space.
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F4
When we connected the heads of the three screws (one S1 pedicle screw and two S2 alar-iliac screws) with the rod, the three screw heads were tightly touching each other due to the posterior narrow sacral space (Fig. 4).