Metal Hypersensitivity Reactions Following Spinal Implants

BACKGROUND: Metal hypersensitivity reactions are infrequently reported but clinically significant after spinal implant surgery. Clinical presentation can mimic infection or mechanical failure, making diagnosis difficult. Evidence to guide diagnosis and management is largely limited to short case series and case reports. The purpose of this study was to systematically review the clinical presentation, diagnostic methods, and outcomes of metal hypersensitivity associated with spinal implants. METHODS: A systematic review was conducted of PubMed, Embase, and Scopus from inception through June 22, 2026, in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Title and abstract screening, full-text review, and data extraction were performed independently by 2 reviewers with conflicts resolved by a third reviewer. Eligible studies included adult patients with suspected or confirmed metal hypersensitivity following spinal implant surgery that reported patient-level clinical outcomes. RESULTS: Fifteen studies with a total of 19 patients met inclusion criteria (53% female, 42% male, and 5% not reported). The median patient age was 47 years (range, 19-69). Twelve procedures (63%) were fusion-based, while 7 (37%) were motion preserving, including disk arthroplasty and artificial facet replacement systems. Common clinical presentations included persistent pain, with 8 patients (42%) exhibiting dermatologic manifestations. Metal hypersensitivity was immunologically confirmed by positive patch testing and/or lymphocyte transformation testing in 11 patients (58%), while 8 (42%) were diagnosed clinically. Onset of symptoms ranged from immediately postoperatively to 15 years after implantation. Eighteen patients underwent removal or revision with clinical improvement in 14 of 16 with a reported outcome (88%). CONCLUSION: Metal hypersensitivity reactions following spinal implants are infrequently reported but may present either immediately or in a delayed manner with symptoms that mimic more common postoperative complications, such as infection or pseudarthrosis, or may present with dermatologic manifestations. In cases where other etiologies are ruled out, hardware removal was frequently, though not invariably, associated with clinical improvement, which was reported narratively rather than by validated outcome measures. LEVEL OF EVIDENCE: Therapeutic Level V. See Instructions for Authors for a complete description of levels of evidence.