Fig. 1
(A, B) Sacral dysmorphism represents the acute angulation of sacral ala and reduced the corridor for iliosacral screw fixation. ^*Cortical perforation of screw.

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Fig. 2
(A) Posterosuperior corners of sacrum were connected by imaginary line. Asterisks: body of 1st sacrum. (B) The virtual cylinder for ilio-sacral screw was placed according to the curve point. (C) the curve point could be visualized easily without additional support.

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Fig. 3
(A) Lateral radiographs showed the safe zone of 1st and 2nd sacrum. (B, C) The conventional ilio-sacral screw was placed toward the opposite corner of superior endplate.

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Fig. 4
(A–C) The trans-sacral trans-iliac screw should be placed transversely just below the ICD line. (D, E) The entry point was placed just anterior to the curve point. (F, G) The screw did not pierce the cortex around the sacral canal and foramen.

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Fig. 5
(A) Unstable pelvic ring injury in a 20-year-old male showing the involvement of spinal canal and comminution of upper sacral surface. (B) The trans-sacral trans-iliac screw was performed after the anterior fixation for achieving the functional reduction of sacrum. (C) The radiographs after 12 months showed neither a loss of reduction nor screw back-out.

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Fig. 6
(A, B) The variable of basal height could be measured using the three-dimensional biplanar image in the opposite side.

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Fig. 7
(A, B) The safe zone of the 2nd sacrum can be observed easily in the lateral radiographs of pelvis and increased inversely according to the sacral dysmorphism.

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Fig. 8
(A–C) A 63-year-old male sustained an unstable pelvic injury with spino-pelvic dissociation. (B, C) The spino-pelvic fixation was performed and showed the iliac screw, which was used with the connecting rod. (D) The radiograph after 12 months showed the maintenance of pelvic ring.

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Fig. 9
(A–C) S2 alar-iliac (S2AI) screw should be toward the AIIS and passed just over the superior rim of the greater sciatic notch, above the greater sciatic notch. (D) The screw trajectory was from the dorsal cortex of the sacrum to the inner ilium by penetrating the sacro-iliac joint.

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Fig. 10
(A) A 57-year-old male sustained an unstable pelvic injury with L5 body fracture. (B) First, the pedicle screw of L4 and L5 was placed percutaneously and made the entry portal for the S2 alar-iliac (S2AI) screw. (C) The postoperative radiographs showed the functional reduction of the pelvis. (D) Follow-up radiographs at eight weeks showed the maintenance of reduction adequacy.

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Fig. 11
(A) A 71-year-old female sustained of an unstable pelvic injury (sacral fracture). (B–D) The PTB plate fixation was performed and the osseous corridor was used to achieve the maximal screw length. (E–H) The postoperative radiographs showed an acceptable reduction of the pelvis. (I) The follow-up radiographs at 12 months showed the maintenance of reduction.

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