Clinical outcomes of S2 Alar-Iliac screw technique in the treatment of severe spinal sagittal imbalance: a retrospective 2-year follow-up study


  • Yao Zhao Department of Orthopaedics, Peking University First Hospital, Beijing, China
  • Jianchuan Shu Department of Orthopaedics, Peking University First Hospital, Beijing, China
  • Longtao Qi Department of Orthopaedics, Peking University First Hospital, Beijing, China
  • Chengxian Yang Department of Orthopaedics, Peking University First Hospital, Beijing, China
  • Beiyu Xu Department of Orthopaedics, Peking University First Hospital, Beijing, China
  • Zhengrong Yu Department of Orthopaedics, Peking University First Hospital, Beijing, China
  • Chunde Li Department of Orthopaedics, Peking University First Hospital, Beijing, China



Adult spinal deformity, Severe sagittal imbalance, S2AI screw, Mechanical complication, PI-LL


Background: The treatment of adult spinal deformity (ASD) remains a significant challenge, especially in elderly patients. This study aimed to evaluate the outcomes of the S2AI screw technique in the treatment of severe spinal sagittal imbalance with a minimum 2-year follow-up.

Methods: From January 2015 to December 2018, 23 patients with severe degenerative thoracolumbar kyphosis who underwent placement of S2AI screws for long segment fusion were retrospectively reviewed. Patients were divided into group A (no mechanical complications, 13 cases) and group B (with mechanical complications, 10 cases) according to the occurrence of mechanical complications at the last follow-up. Radiographic parameters were compared between groups preoperatively, 1 month postoperatively and at the last follow-up. Risk factors for mechanical complications were analyzed.

Results: The incidence of mechanical complications was 43.5% and the revision rate was 17.4%. At 1 month postoperatively, sagittal correction was better in group A than in group B (p<0.05). The area under the curve for predicting mechanical complications of sacral slope (SS), lumbar lordosis (LL), PI (pelvic incidence)-LL at 1 month postoperatively were 0.762 (p=0.035), 0.896 (p=0.001) and 0.754 (p=0.041) respectively and the best cut-off values were 24.1°, 32.8°and 12.0°. The sagittal correction of both groups was partially lost at the last follow-up.

Conclusions: A high incidence of mechanical complications was observed in long-segment corrective surgery with the S2AI screw technique for severe spinal sagittal imbalance. Inadequate sagittal correction is a risk factor for the development of mechanical complications.



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