Intraoperative and postoperative changes of pelvic incidence in patients with degenerative spinal deformity treated with S2 alar-iliac screw fixation

English Keywords:Degenerative spinal deformity  Pelvic fixation  Spinal correction  Pelvic incidence  Sacroiliac joint  S2 alar-illac screw

English Abstract:

  【Abstract】 Objectives: To investigate the changes of pelvic incidence(PI) during and after S2 alar-iliac(S2AI) screw fixation in patients with degenerative spinal deformity. Methods: Patients with degenerative spinal deformity who received posterior long segment fusion and fixation in our hospital from November 2016 to October 2020 were retrospectively analyzed. Among them, 22 patients underwent bilateral S2AI screw fixation distal to pelvis, including 3 males and 19 females, aged 45-74 years(62.3±7.9 years). Computer-assisted O-arm navigation system was used to guide screw placement. The full-length standing anteroposterior and lateral X-ray images before operation, 1 week after, and at the final follow-up were collected, and Cobb angle, PI, lumbar lordosis(LL), value of PI-LL, pelvic tilt(PT), sacral slope(SS), sagittal vertical axis(SVA) were measured at each time point. The sagittal images of pelvis of patients in the prone position scanned by O-arm navigation system during operation were exported, and the values of PI, PT, and SS were measured. Results: The number of fixed segments in 22 patients was 5-17(11.1±2.21), and the follow-up period was 5-13 months(6.64±1.43 months). At preoperation, postoperation and final follow-up, the values of imaging parameters were respectively, the Cobb angles: 38.04°±21.12°, 19.16°±12.49°, and 19.01°±11.99°; LL: 28.48°±28.12°, 40.61°±15.25°, and 39.25°±15.51°; SVA: 75.64±64.66mm, 21.82±19.42mm, 23.18±19.12mm; PI: 5.55°±14.68°, 50.47°±13.35°, and 53.94°±13.37°; PI-LL: 27.10°±22.00°, 9.86°±10.41°, and 12.92°±13.02°; PT: 31.55°±10.25°, 19.69°±7.7°, and 24.25°±8.28°; SS: 24.00°±16.61°, 30.78°±10.27°, and 29.55°±11.23°. The Cobb angle, LL, SVA, PI, PI-LL, PT and SS at postoperative 1 week and the last follow-up were significantly different from those before operation(P<0.05), and the PI and PT at the last follow-up were with significant differences from those at 1 week after operation(P<0.05). The intraoperative PI, PT and SS were 45.17°±14.20°, 21.56°±6.71°, and 23.61°±12.86°, respectively, of which, PI and PT were significantly different from those at preoperation, 1 week after operation and the final follow-up(P<0.05), while intraoperative SS was not statistically different from that before operation(P>0.05), yet it was with significant difference from postoperative 1 week and the last follow-up(P<0.05). In 21 patients(95%) the intraoperative PI decreased by more than 5° compared with that before operation, and in 13 patients(59%) the postoperative PI in standing position decreased by more than 5° compared with the preoperative PI. Conclusions: Patients with degenerative spinal deformity treated with S2AI screws had a significant decrease in intraoperative PI in prone position comparing with preoperative PI in standing position, and the postoperative PI in standing position was smaller than the preoperative PI in standing position although it was bigger than the intraoperative PI.