Which are the most frequently used outcome instruments in studies on total ankle arthroplasty?

The number of studies reporting on outcomes after total ankle arthroplasty is continuously increasing. As the use of valid outcome measures represents the cornerstone for successful clinical research, we aimed to identify the most frequently used outcome instruments in ankle arthroplasty studies and to analyze the evidence to support their use in terms of different quality criteria. A systematic review of the literature identified 15 outcome instruments reported in 79 original studies. The most commonly used measures were the American Orthopaedic Foot and Ankle Society hindfoot score (n = 41), the Kofoed ankle score (n = 21), a visual analog scale assessing pain (n = 15), and the generic SF-36 (n = 6). Eight additional instruments were used only once or twice. The American Orthopaedic Foot and Ankle Society and Kofoed instruments include a clinical examination and score up to 100 points. Evidence to support their use in terms of validity, reliability, responsiveness, and interpretability is limited, raising the question whether their use is justified. Self-reported questionnaires related to ankle osteoarthritis or arthroplasty are rather disregarded in the current literature, and only the Foot Function Index is associated with evidence in terms of the above-mentioned quality criteria. Future research is warranted to improve the outcome assessment after total ankle arthroplasty.