Long-term patient-reported outcomes and mechanical complications following spinal fusion in patients with surgical site infection managed with retained instrumentation versus non-infected patients: a systematic review and meta-analysis.

Background: Spinal fusion is frequently performed for degenerative and deformity spinal disorders, and surgical site infection (SSI) is one of its most consequential postoperative complications. Although implant retention is often pursued to preserve spinal stability and alignment, the impact of SSI on patient-reported outcome measure (PROM) and mechanical complications compared with non-infected patients is incompletely explored. This study aims to compare pain, disability, and mechanical outcomes between adult spinal fusion patients with SSI managed by retained instrumentation and non-infected controls. Methods: This systematic review and meta-analysis were registered in PROSPERO. PubMed, Embase, Scopus, and Web of Science were searched from inception through December 2025. Eligible studies included adult cohorts undergoing instrumented spinal fusion with SSI treated by implant retention and a non-infected comparison group. Primary outcomes were changes in Visual Analog Scale (VAS) scores and Oswestry Disability Index (ODI), representing PROM. Secondary outcomes included unplanned readmission, revision surgery excluding debridement, pseudarthrosis, and proximal junctional kyphosis (PJK). Random-effects models were used to calculate standardized mean differences and odds ratios (ORs). Results: Eleven studies comprising 2,681 patients were included, with mean follow-up of 33.9 months (range, 22-70.7 months). Improvements in back pain VAS, leg pain VAS, and ODI did not differ significantly between SSI and non-SSI groups, showing comparable long-term functional recovery. In contrast, SSI managed with retained instrumentation was associated with significantly increased odds of unplanned readmission, revision surgery excluding debridement, and pseudarthrosis. No significant difference was observed in PJK. Substantial heterogeneity was present for several mechanical outcomes. Conclusions: In adult spinal fusion, patients with SSI managed with retained instrumentation demonstrated patient-reported outcomes comparable to non-infected controls. However, SSI is associated with increased mechanical complications and healthcare utilization. These findings support intensified surveillance, risk-adjusted counseling, and standardized outcome reporting for patients experiencing SSI after spinal fusion.