Radiographic and Clinical Analysis of the INBONE II Total Ankle Arthroplasty

Abstract

Category: Ankle Arthritis; Ankle Introduction/Purpose: The use of total ankle arthroplasty (TAA) in the treatment of ankle arthritis has grown substantially as advancements are made in design and surgical technique. Among the criteria guiding the choice between arthroplasty versus arthrodesis, the long-term survival and postoperative outcomes are of crucial importance. First FDA approved in 2005, the INBONE I prosthesis was subsequently replaced by the INBONE II in 2010. While outcomes of the INBONE I have been published, there is limited long-term survivorship data for the INBONE II. The purpose of this study is to determine the minimum 5-year survivorship of the INBONE II prosthesis and causes of failure. In addition, we evaluate long-term radiographic and patient- reported outcomes. Methods: We retrospectively identified 46 prospectively followed patients from 2010 to 2015 who underwent TAA with the INBONE II prosthesis at our institution. Of these, 44 cases (41 patients) had minimum follow-up of 5 years (mean, 6; range, 5 to 9). Mean age was 65.6 years (range, 42 to 81) and mean BMI was 27.6 (range 20.1 to 33). Survivorship was determined by incidence of revision, defined as removal/exchange of a metal component. Chart review was performed to record incidences of revision and reoperation. Preoperative, immediate and minimum 5-year x-rays were reviewed; coronal tibiotalar alignment (TTA) was measured on standing AP radiographs to assess alignment of the prosthesis. A TTA of +-5° from 90° indicated neutral alignment, while 95° was considered varus and valgus alignment, respectively. Radiographic subsidence as well as presence and location of periprosthetic cysts were documented. Pre- and minimum 5-year FAOS domains were compared. Results: Survivorship was 97.7% with one revision of the talar component due to aseptic loosening and subsidence. The rate of other reoperations was 4.5% (2); one patient underwent medializing calcaneal osteotomy for valgus heel alignment, another patient underwent ostectomy and debridement for ankle impingement. Average preoperative TTA was 88.5 degrees with 15 neutral (average TTA of 89.7°), 14 varus (74°) and 12 valgus (104°) ankles. Average postoperative TTA was 88.6° with 35 neutral (89.3°), 6 varus (84.7°), and no valgus ankles. Radiographic subsidence was observed in one patient who underwent revision, and periprosthetic cysts were observed in 7 patients. There was significant improvement in all FAOS domains at final follow-up. Conclusion: This is the largest study to date dedicated to evaluating survivorship of the INBONE II prosthesis. Our data suggests a high survival rate and low reoperation rate with long-term follow-up of the INBONE II implant. We observed significant improvement in radiographic alignment as well as patient-reported clinical outcomes at minimum 5-year follow-up.