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Introduction/Purpose: Tantalum coated metal spacers (TCMS) have recently been utilized to fill and provide structure to large bony defects in the hindfoot. Tantalum is an appealing material due to its biocompatibility, lack of immune response generation, and structural integrity. Compared to custom printed spacers and bulk allografts, TCMS are readily available off-the-shelf implants with significantly less cost. There is currently a paucity of literature assessing the use and outcomes of TCMS in foot and ankle surgery, specifically in tibiotalocalcaneal (TTC) arthrodesis. This study serves to assess clinical outcomes and fusion rates of patients who underwent TTC arthrodesis utilizing intramedullary nailing with TCMS augmentation for large bony defects. Methods: We retrospectively identified all patients > 18 years of age who underwent TTC arthrodesis with TCMS augmentation at our tertiary care center between 2015-2021. We also identified all patients who underwent TTC arthrodesis without augmentation within that time frame. The computed tomography (CT) scans at the six-month postoperative point were reviewed by one board-certified orthopaedic foot and ankle surgeon to determine fusion status, which was defined as having at least 50% fusion mass. Patient-reported outcomes measures (PROMs) including the modified foot function index (FFI) and PROMIS Global Mental Health Score were collected for patients in both groups. Patient demographics, clinical outcomes, and PROMs were compared between groups. A multivariate logistic regression model measured the effect of TCMS augmentation on the likelihood of achieving fusion. Results: Of the 65 patients included, 21 patients (32.3%) underwent TTC with TCMS augmentation. There were no significant differences in demographics between the two groups. Patients in the TCMS group had significantly higher modified FFI (91.1 + 47.6 vs 26.3 + 48.8, p< 0.001) and PROMIS Global Mental Health (12.2 + 4.82 vs. 5.59 + 6.76, p< 0.001) scores in the postoperative period. Overall, the fusion rate was higher for the TCMS group, however the difference was not significant between groups (90.5% vs. 80.5%, p=0.472). Multivariate logistic regression identified that TCMS augmentation was a nonsignificant predictor of increased odds of fusion at the six-month postoperative point (OR=2.87, p=0.232). Conclusion: This study is the largest to date to present 6-month postoperative CT scans demonstrating successful TTC fusion with TCMS augmentation, contributing to our understanding of its utility. Given the severity of disease and bone loss in the TCMS group, it is not surprising that post-operative patient reported outcome scores differed significantly compared to the control group. TCMS augmentation can be utilized as cost effective spacers to fill large defects in TTC arthrodesis with successful union rates. Further studies are needed to evaluate the efficacy of TCMS augmented fusions as a viable substitute to custom printed cages. [ABSTRACT FROM AUTHOR]