Study design: Retrospective observational cohort study.
Objective: To determine change in pelvic incidence (PI) and loss of correction after long fusion with iliac screws, the effect of iliac screw loosening, and global alignment according to postoperative PI.
Summary of background data: Posterior long fixation and fusion of the thoracic to the ilium is one of the most common surgical treatments for adult spinal deformity (ASD). Long fusion to the sacrum with iliac screws decreases the PI by 3.9° after surgery. PI decreases once by long fusion with iliac screws. However, if the iliac screw loosens, PI may cause correction loss and return to the preoperative PI.
Methods: We retrospectively reviewed the cases of 69 consecutive patients with ASD. Their mean age (SD) was 70.5 (7.3) years, 12% were male. PI was evaluated preoperatively, early- and 1-year postoperatively. We compared change in PI with and without loosening of iliac screws, spinopelvic parameters according to 1-year-postoperative PI.
Results: PI decreased significantly from 51.8° (9.3°) to 48.1° (9.5°) early postoperatively (P < 0.01). PI increased significantly from 48.1° (9.5°) to 49.6° (9.7°) within a year postoperatively (P < 0.01). Significant loss of PI correction (2.3°, P < 0.01) occurred within a year after surgery in patients with iliac screw loosening and was significantly different from the PI loss in those without screw loosening (53.9°, 48.2°, P = 0.03). Pelvic tilt, sacral slope, C7 sagittal vertical axis, global tilt, and T1 pelvic angle were significantly smaller in the group with PI <50° postoperatively at 1 year compared with the group with PI >50°.
Conclusion: Although PI decreases after long fusion surgery with iliac screws, significant correction loss appears within a year. Loosening of iliac screws may exacerbate this loss. Patients with PI <50° postoperatively were able to maintain better global alignment.
Level of evidence: 3.