A COMPARISON OF PROSPECTIVE OUTCOMES OF INFINITY TOTAL ANKLE ARTHROPLASTY VERSUS ANKLE FUSION

Introduction: Ankle fusion (AF) or Total ankle arthroplasty (TAA) can be used to treat end stage ankle arthritis (ESAA). TAA has become more reliable in modern generations with patient specific instrumentation, improvement in polyethylene and ingrowth surfaces. The INFINITY® Total Ankle System (Stryker Inc.) is a 2-component fixed-bearing, bone-sparing modern design introduced in 2014. The purpose of this study is to compare prospective outcomes of Infinity ankles (outcome scores and revision rates) with ankle fusion. Method: 100 patients with prospectively collected data having an INFINITY® TAA between 2013- August 1st, 2021, were compared with 200 ankle fusion patients from 2008 -August 1st, 2021 with a minimum 1 year follow up. The primary outcome was the Ankle Osteoarthritis Scale (AOS). Secondary outcomes were the MODEMS, and SF-36 scores. The average was 5.1 years, and the follow up was 5.9 years for AF and 3.4 years for TAA. Results: Ankle Fusion AOS scores improved from a preoperative average of 55.25±19.31, to 26.01±21.64. TAA scores improved from 52.37±19.09 to 22.33±21.41 for TAA. At the last follow up after surgery (LFU), mean AOS scores in the Infinity cohort were significantly lower after linear regression for baseline variables with a mean difference of −6.76 (−12.52, −0.99 95% CI) p-value 0.02. The difference remained significant after removing 1-year follow up, and 9–14 year follow up, at −6.58 (−12.89, −0.27 95% CI), p-value 0.041. The revision rate for ankle fusion was 3.5%, while revision rate for INFINITY® TAA was 2%. Conclusion: Patients undergoing INFINITY® TAA had significantly lower mean AOS scores than patients undergoing ankle fusion at their last follow up after surgery, both before and after linear regression for baseline variables. This remained significant after excluding earlier (1-year) follow up, and later (9-14 year) follow up for the fusion cohort data. Modern ankle replacement designs continue to improve compared against the ankle fusion gold standard.