A Comparative Analysis of Subtalar and Ankle Arthrodesis in Patients With and Without Prior Ipsilateral Fusion

Research Type: Level 3 - Retrospective cohort study, Case-control study, Meta-analysis of Level 3 studies Introduction/Purpose: Subtalar arthrodesis is a widely performed procedure for managing arthritis, calcaneal fractures, deformities, and instability of the hindfoot. Some studies suggest that prior ankle arthrodesis may negatively impact subtalar fusion due to altered joint biomechanics and vascular supply, but evidence remains limited. Few direct comparisons exist between patients with and without prior ankle fusion, leaving uncertainty about its true effect on fusion outcomes. This study, one of the largest of its kind, examines subtalar fusion rates in patients with and without previous ipsilateral ankle arthrodesis. A secondary objective of this study is to examine ankle fusion rates in patients with and without previous ipsilateral subtalar arthrodesis. Methods: This retrospective study utilized data from the TriNetX Research Network to identify patients who underwent a subtalar fusion with (primary ankle + subtalar) and without (subtalar-only) previous ipsilateral ankle arthrodesis between February 20, 2004, and February 20, 2024. A secondary analysis examined those who underwent an ankle fusion with (primary subtalar + ankle) and without (ankle-only) previous ipsilateral subtalar arthrodesis. Patients with a previous nonunion diagnosis or less than one year of follow-up were excluded. Propensity score matching (1:1) controlled for age, sex, BMI, and several comorbidities. Primary outcomes included one-year rates of nonunion and hardware removal. Risk differences with 95% confidence intervals were calculated, and significance was determined using Z-tests (p < 0.05). Results: Before matching, there were 162 patients in the primary ankle + subtalar group and 10,144 patients in the subtalar-only group. Additionally, there were 131 patients in the primary subtalar + ankle group and 5,032 patients in the ankle-only group. There were no significant differences in orthopaedic complications between the primary ankle + subtalar group and subtalar-only groups, including rates of nonunion (14.3% vs. 20.5%, p = 0.142) and hardware removal (15.5% vs. 12.4%, p = 0.422). In the secondary analysis between the primary subtalar + ankle and ankle-only groups, there were no significant differences in nonunion rates (10.0% vs. 15.4%, p = 0.192) or rates of hardware removal (16.2% vs. 12.3%, p = 0.375). Conclusion: This study found no significant differences in nonunion or hardware removal rates between patients undergoing subtalar arthrodesis with and without prior ipsilateral ankle fusion. Similarly, in the secondary analysis, prior subtalar fusion did not significantly impact ankle arthrodesis outcomes. These findings suggest that previous arthrodesis at an adjacent joint does not increase the risk of nonunion or hardware-related complications in subtalar or ankle fusion procedures. Given the lack of evidence for a negative impact, surgeons may view prior ankle or subtalar arthrodesis as less of a contraindication when planning fusion procedures, allowing for greater flexibility in surgical decision-making.