A Retrospective, Comparative Study on Infinity Ankle Replacements vs Ankle Fusions

Category: Ankle Arthritis; Ankle Introduction/Purpose: End-stage ankle arthritis (EAA) can diminish quality of life and handicap one’s daily activities. Ankle fusion or Total ankle arthroplasty (TAA) are two surgeries used to treat EAA. While ankle fusion has traditionally been the treatment of choice, it often impairs ankle functionality, and can increase the development of painful hindfoot arthritis. TAA typically has shorter recovery time and wider range of motion. Historically, TAA prostheses were inadequate due to frequent failures. Modern design and techniques have improved outcomes, decreased failure rates, allowed more normalized gait, and reduced adjacent joint arthritis development, but long-term performance remains ill-defined. The INFINITY ® Total Ankle System (Stryker Inc.) is a 2-component fixed-bearing, bone-sparing design that this study aims to compare to ankle fusion through patient reported outcomes. Methods: Patients at least 19 years old at the time of index procedure were selected. We compared 100 patients who had the INFINITY ® TAA between 2013- August 1st, 2021, with 200 ankle fusion patients from 2008 -August 1st, 2021, all with minimum 1 year of follow up. The primary outcome was the Ankle Osteoarthritis Scale (AOS). Secondary outcomes were the MODEMS, and SF-36 scores. Revision fusion and revision INFINITY ® patients were excluded. Results: At 1 year follow up, Ankle Fusion AOS scores improved from a preoperative average of 55.25±19.31, to 26.01±21.64, vs 52.37±19.09 to 22.33±21.41 for INFINITY ® 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 that only had fusion cohort data.