Postoperative MRI Artifact Burden After Carbon Fiber-Reinforced PEEK Versus Titanium Instrumentation in Metastatic Spinal Disease

Background/Objectives: Patients undergoing surgery for metastatic spinal disease often require instrumented stabilization followed by radiotherapy and postoperative magnetic resonance imaging (MRI) surveillance. Titanium implants may generate artifacts that impair assessment of the operated level, whereas carbon fiber-reinforced polyetheretherketone (CFR-PEEK) constructs may improve MRI assessability. This study compared CFR-PEEK and titanium instrumentation with respect to postoperative MRI artifact burden, early outcomes, and oncological follow-up, and introduced a study-specific artifact grading system. Methods: This retrospective single-center cohort included 78 patients treated with instrumented stabilization for metastatic spinal disease: 33 with CFR-PEEK and 45 with titanium instrumentation. Postoperative MRI suitable for artifact assessment was available in 47 patients. Implant-related artifacts were evaluated using the Oncologic Spinal Instrumentation MRI Artifact Score (O-SIMAS), a 0–5 anatomy-based grading system. Early postoperative outcomes, local recurrence, progression-free survival, overall survival, and interrater agreement were analyzed. Results: CFR-PEEK instrumentation was associated with lower postoperative MRI artifact burden than titanium instrumentation, with median O-SIMAS scores of 2.0 versus 3.0, respectively (p < 0.001). High-grade artifacts were less frequent after CFR-PEEK than after titanium instrumentation (15.8% versus 67.9%; p = 0.0008). Titanium instrumentation remained independently associated with high-grade artifacts. Early postoperative outcomes, local recurrence, progression-free survival, and overall survival did not differ significantly between groups. O-SIMAS showed substantial pairwise interrater agreement. Conclusions: CFR-PEEK instrumentation was associated with improved postoperative MRI assessability and fewer diagnostically relevant artifacts than titanium instrumentation. No oncological benefit was shown. O-SIMAS may support structured artifact assessment, but requires external validation.