Clinical Outcomes Associated with Screw Loosening in S2 Alar-Iliac Fixation in Adult Spinal Deformity

<b>Purpose</b>: To explore the clinical outcomes associated with screw loosening after S2 alar-iliac (SAI) screw fixation for adult spinal deformity (ASD). Overview of the literature: SAI fixation is widely used in ASD corrective surgery; despite the biomechanical advantages of this screw, complications such as screw loosening remain a significant concern. <b>Methods</b>: We retrospectively reviewed 27 patients undergoing corrective surgery for ASD using SAI as the distal fixation point at a single institution between February 2013 and February 2018. Patients were divided into non-loosening (N) and loosening (L) groups based on radiological evidence of screw loosening (radiolucent area of 1 mm around the screw) and compared for demographic characteristics, bone mineral density (T-score), spinal alignment parameters, and patient-reported outcome using the Japanese Orthopaedic Association Back Pain Evaluation Questionnaire (JOABPEQ) scores. <b>Results</b>: Screw loosening was observed in 78% of patients (n = 21/27); however, there were no statistically significant differences between the N and L groups in terms of the preoperative and 5-year postoperative JOABPEQ scores (<i>p</i> > 0.05 across all domains) and spinal sagittal alignment (<i>p</i> > 0.05). The improvements achieved through corrective surgery were largely maintained regardless of the presence of screw loosening. <b>Conclusions</b>: SAI screw loosening is a common sequela in ASD surgery; however, its loosening might not affect long-term clinical outcomes. Therefore, the choice of fixation should be individualized based on patient factors such as age and bone quality.