The arthritic pathology of the tibio-tarsal joint has a prevalence of approximately 1% in the general population, and its incidence has been increasing over the years. Advanced-stage arthritis causes pain, impairs mobility, and has an extremely negative impact on patients' quality of life, resulting in significant social and economic costs. Unlike hip and knee arthritis, ankle arthritis is often secondary to traumatic events, affecting younger patients. An emerging treatment for severe ankle arthritis is ankle prosthetic replacement, and patient-reported outcome measures (PROMs) are increasingly used to assess patient outcomes. The study focuses on the validity and reproducibility of the Italian versione of the Forgotten Joint Score (FJS) in ankle prostheses, obtained through the translation-back-translation method, with a sample size of 120 patients.