PMC9245539_01
Case 1. (a) Preoperative antero-posterior (AP) views of bilaterally fused hips. (b) Pelvic hyperextension calculation. (c) Six months postoperative antero-posterior (AP) view of the pelvis.
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F1
His left hip was fused in 15  of flexion, 30  of abduction, and 20  of external rotation (Figure 1a). Preoperative radiographs and CT scans showed fibrous ankylosis of both hips and pelvic hyperextension of approximately 26.7  (Figure 1b). There were no complications at the 20-month of follow-up (Figure 1c).
PMC9245539_02
Case 5. (a) Preoperative antero-posterior (AP) view (bony ankylosis of right hip). (b) Six months antero-posterior (AP) view of the pelvis. (c) and (d) Preoperative planning for case 5 in transverse and sagittal plane. (e) Verification of pelvic rotation by localizing the anterior superior iliac spine with the hip probe.
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F2
Indications for surgery were a sub-optimally fused position and functional impairment (Figure 2a). The subsequent 32 registration points should be widely distributed over the ilium, femoral neck, and the ischium and registered over the hard cortical bone (Figure 2e). Afterwards, the eight verification points are taken to confirm the rotational alignment; while doing so, the surgeon can position the probe over the anterior superior iliac spine to verify the rotation (Figures 2c and 2d). There were no complications at the 16-month follow-up (Figure 2b).