Midterm Clinical Outcomes, Radiographic Outcomes, and Survivorship of the Infinity Total Ankle Arthroplasty

Background: The Infinity Total Ankle Arthroplasty (Stryker, Mahwah, NJ) is a low-profile fixed-bearing implant first introduced in 2014. Although the short-term survivorship (2-4 years follow-up) and complication rates of the Infinity TAA have been reported, there are limited midterm outcome reports. The aim of this study was to describe the survivorship and clinical outcomes of a single-center experience with the Infinity implant at minimum 5-year follow-up. Methods: Retrospective review of 65 ankles that underwent primary total ankle arthroplasty (TAA) with the Infinity implant was conducted. Mean clinical follow-up was 6.5 years (range, 5.0-8.0). Preoperative and postoperative radiographs were measured to assess tibiotalar alignment, periprosthetic lucencies, and cysts. Preoperative, 2-year, and 5-year postoperative Foot and Ankle Outcome Score (FAOS) subscores were compared to assess midterm clinical outcomes. Survivorship assessment was determined by removal of 1 or both metallic implant components. Results: Survivorship of the implant was 93.8% at final follow-up. There were 4 revisions: 2 for tibial implant loosening, 1 for talar loosening, and 1 for loosening of both components. Three of the 4 revisions occurred within the first 2 years following implantation, and the last failure occurred at 7 years postoperatively. There were 11 reoperations in 10 (15%) ankles and 3 wound complications. There were 17 ankles (26.2%) with radiographic abnormalities around the implants, including 14 cases with tibial component lucencies and 4 cases of periimplant cysts. FAOS outcome measurement showed general stability between 2 and 5 years and substantial improvement from preoperative status. Conclusion: To date this study is the largest midterm report on the Infinity total ankle prosthesis, with 65 implants at a mean follow-up of 6.5 years. We found good midterm implant survivorship, and patients experienced significant improvements in FAOS outcome scores and radiographic alignment at final follow-up.