Ankle Arthrodesis Associated With Risk of Progression to Total Knee Arthroplasty Compared to Total Ankle Arthroplasty

Background: It is unknown how the increased range of motion and improved gait mechanics provided by total ankle arthroplasty (TAA) affects the progression of knee arthritis compared with ankle arthrodesis (AA). We hypothesized that patients treated with TAA would have a lower incidence of postoperative knee arthritis and total knee arthroplasty (TKA) compared with AA. Methods: We retrospectively reviewed a matched cohort of 3751 AAs and 3751 TAAs performed between January 1, 2007, and December 31, 2021, using a commercial claims database. Patients with a history of preoperative knee arthritis or TKA were excluded. Patients were matched 1:1 for gender, age at time of ankle surgery, indication for ankle surgery, year of ankle surgery, and geographical region. Univariate and multivariate regression analyses were performed. Significance was set at P < .05. Results: Demographics were similar between AA and TAA. AA (absolute risk AR = 17.54%, odds ratio OR = 1.24, CI = 1.07-1.44), earlier years of ankle surgery, and older age increased the risk of postoperative knee arthritis compared with TAA (AR = 10.10%, absolute risk reduction ARR = 7.44%, CI = 5.89%-8.99%). Posttraumatic ankle arthritis, inpatient surgery, and surgery in the West region were protective against developing postoperative knee arthritis. AA (AR = 4.19%, OR = 2.37, CI = 1.65-3.39), earlier year of ankle surgery, males, and other indication for ankle surgery increased the risk of requiring a postoperative TKA compared with TAA (AR = 1.36%, ARR = 2.83%, CI = 2.09%-3.57%). Posttraumatic ankle arthritis and inpatient surgery were protective factors against requiring a TKA. Conclusion: There is a significantly higher incidence of patients who underwent TKA after AA compared with TAA, although the inability to confirm laterality in 38% of cases dilutes the hypothesis of a specific biomechanical association in the study. We recommend that surgeons carefully weigh the risks and benefits of TAA and AA with this in mind, especially in patients with minimal knee arthritis, as a potential strategy to mitigate risk of requiring TKA in the future. Level of Evidence: Level III, retrospective comparative study.