Long fusion to the sacrum with iliac screws can decrease pelvic incidence (PI). Considering the physiological range of movement of the sacroiliac joint, this decrease may be relatively extreme. The purpose of the study was to determine changes in pelvic morphology after orthopedic surgery using long fusion with iliac screws, and examine the relationship between changes in PI and morphology. We included data from 80 consecutive patients who underwent corrective surgery for adult spine deformity (72 female and 8 male; mean age: 71.1years). We examined preoperative and early postoperative full-standing X-ray images and pelvic computed tomography of the patients and compared the following: (1) pre- and postoperative pelvic measurements including PI, (2) correlations between change of PI, iliac angle, and distance between posterior superior iliac spines (DPSIS). After surgery, PI decreased significantly ( 3.3 , 95% confidence interval [95%CI] 4.3 to 2.3 , P 0.01) and DPSIS increased significantly (+ 2.7mm, 95%CI 1.7 to 3.8mm, P 0.01). By contrast, iliac angle decreased significantly ( 1.4 , 95%CI 2.1 to 0.7 , P 0.01). There were significant correlations between changes of PI and iliac angle (r = 0.34, P 0.01) and between changes of DPSIS and iliac angle (r = 0.44, P 0.01). We observed changes in pelvic morphology associated with spinal pelvic correction surgery using iliac screws and changes in pelvic incidence related to these changes in pelvic morphology. We recommend selecting pelvic anchors and surgical procedures considering potential movement of the sacroiliac joint. These slides can be retrieved under Electronic Supplementary Material.
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