Long fusion to the pelvis with S2-alar-iliac screws can induce changes in pelvic incidence in adult spinal deformity patients: analysis of predictive factors in a retrospective cohort

Eur Spine J. 2019 Jan;28(1):138-145. doi: 10.1007/s00586-018-5738-2. Epub 2018 Aug 24.


Purpose: To verify whether pelvic incidence (PI) would change in adult spinal deformity (ASD) patients who underwent long instrumentation using S2-alar-iliac (S2AI) screws and to identify factors associated with the change in PI.

Methods: We retrospectively reviewed all patients who underwent spinal surgery using S2AI screws between November 2014 and January 2017 at our institution. Patients aged 20 years or above with available radiographs were included. According to the change in PI, patients were divided into two groups, group C: PI variance reached 5 or more degrees postoperatively and group NC: PI changed less than 5°.

Results: A total of 47 patients (3 males, 44 females; mean age, 52.47 ± 15.80 years) were included in this study. PI significantly decreased from 51.25° ± 14.80° to 40.43° ± 14.23° in group C (n = 26), with a mean change in 11.52° ± 6.17° (P < 0.05), but changed from 47.00° ± 13.18° to 46.57° ± 13.71° in group NC without statistical significance. Intergroup analysis showed that change in PI, preoperative PI-LL, preoperative LL, preoperative SVA, and postoperative PT were significantly different between both groups. Correlation analysis showed that the change in PI and preoperative LL and PI were significantly associated. The formula provided by the regression analysis was ΔPI = - 3.108 - 0.11PreLL + 0.211PrePI.

Conclusions: Our study showed that PI decreased in 55% of ASD patients after spinal surgery using S2AI screws. Greater preoperative PI-LL mismatch and PI, as well as lumbar kyphosis, were associated with postoperative change in PI. These slides can be retrieved under Electronic Supplementary Material.

Keywords: Adult spinal deformity; Long instrumentation fixation; Pelvic fixation; Pelvic incidence; S2-alar-iliac.

MeSH terms

  • Adult
  • Aged
  • Bone Screws*
  • Female
  • Humans
  • Male
  • Middle Aged
  • Pelvic Bones / physiopathology
  • Pelvic Bones / surgery
  • Pelvis* / physiopathology
  • Pelvis* / surgery
  • Retrospective Studies
  • Spinal Curvatures* / epidemiology
  • Spinal Curvatures* / physiopathology
  • Spinal Curvatures* / surgery
  • Spinal Fusion* / instrumentation
  • Spinal Fusion* / methods
  • Spinal Fusion* / statistics & numerical data
  • Young Adult