Introduction: With Japan’s rapidly aging population, corrective spinal fusion surgery for adult spinal deformity (ASD) has increased. ASD surgery is highly invasive, and elderly patients are particularly vulnerable to postoperative complications. Polypharmacy, defined as the use of five or more medications, is common in older adults and may contribute to adverse outcomes. This study aimed to evaluate the effect of polypharmacy on postoperative complications, patient-reported outcome measures (PROMs), and radiographic alignment after ASD surgery.

Methods: A retrospective cohort study was conducted on 394 ASD patients (≥40 years) who underwent corrective surgery between 2010 and 2023. Patients were divided into polypharmacy (PP, n=153) and non-polypharmacy (NP, n=241) groups. Demographics, comorbidities, intraoperative data, complications, PROMs (Oswestry Disability Index [ODI], Scoliosis Research Society-22 [SRS-22]), and radiographic parameters were analyzed. Propensity score matching (PSM) was performed for age and sex.

Results: The PP group had higher rates of comorbidities, greater operative time, and increased revision surgeries, though overall complication rates were not significantly different. Delirium and surgical site infection were the most frequent complications. PROMs were significantly worse in the PP group preoperatively and remained inferior at one- and two-year follow-up (p<0.001). Radiographically, the PP group demonstrated significantly worse sagittal parameters, including pelvic tilt, sagittal vertical axis, and T1 pelvic angle at follow-up. PSM analysis confirmed these trends.

Conclusion: Polypharmacy was not associated with increased overall medical complications but was linked to worse functional outcomes and sagittal alignment postoperatively. As a modifiable risk factor, preoperative medication optimization may improve surgical outcomes in ASD patients.