2025 IFFAS Award for Excellence Winner: Predictive Model for AOS Response in Total Ankle Replacement: Doctor, Will My Symptoms Get Better After the Ankle Replacement?

Research Type: Level 2 - Prospective comparative study, Meta-analysis of Level 2 studies or Level 1 studies with inconsistent results Introduction/Purpose: Ankle osteoarthritis is a condition which generates a level of disability comparable to that of heart failure and chronic kidney failure. To date, no predictive model has been described to determine which patients will experience a more pronounced improvement in disability following total ankle replacement (TAR). Methods: In this prospective cohort study we included all patients between 2003 and 2023 who required a TAR. Revisions and patients who declined to participate in the registry were excluded. A TAR was considered to have a good response if patients showed a difference greater than 31.2 between the initial AOS and the 1–2-year AOS score (Coe et al.,2015). A multivariable logistic regression using a step-wise method was performed, adding or removing variables, and analyzing demographic variables (age at the time of surgery, smoking status, diabetes, inflammatory pathology, and BMI), prosthesis type (Infinity, InBone, InVision, Agility, Hintegra, Mobility, Zimmer, and STAR), etiology, and the AOS at the time of enrollment. As variables were added or removed, the model's AIC was compared, ultimately keeping the most parsimonious version. After model selection, overfitting was evaluated using a bootstrapping method with 1,000 replications, and finally, the goodness-of-fit was assessed by calculating the Brier-Score. Results: A total of 616 total ankle replacements were included. The average age at the time of surgery was 64.84 ± 9.77 years. The most frequently used total ankle replacement was Hintegra (n= 157), followed by Infinity (n= 142), Zimmer (n= 124), and Agility (n= 78). The variables included in the model were the AOS at the time of enrollment (OR 1.07, p < 0.01, 95% CI 1.05–1.08), post-traumatic etiology (OR 0.52, p < 0.01, 95% CI 0.36–0.78), and the Agility prosthesis (OR 0.33, p < 0.01, 95% CI 0.19–0.58). The AUC was 0.79, and when compared using the bootstrapping method, no differences were found, indicating that the model did not show overfitting. Finally, the Brier Score was 0.16, indicating adequate model calibration. Conclusion: In this prospective cohort study, higher AOS scores, meaning more disability at enrollment, were associated with a significantly greater likelihood of achieving clinically meaningful improvement (OR 1.07, p < 0.01). Conversely, post-traumatic etiology (OR 0.52, p < 0.01) and placement of an Agility prosthesis (OR 0.33, p < 0.01) reduced the odds of reaching the predefined threshold of good response. These findings can help guide preoperative discussions with patients regarding expectations after total ankle replacement and the choice of ankle replacement used.