https://doi.org/10.1177/1071100717714953 Foot & Ankle International ® 1–6 © The Author(s) 2017 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/1071100717714953 journals.sagepub.com/home/fai Article Introduction A recent analysis of patient-reported outcome measures (PROMs) for total ankle replacement and ankle arthrodesis procedures demonstrated equivalent reliability and validity of 6 different instruments. 9 Because the common usage of so many different measures undermines the standardization of patient outcome reporting, we sought to develop a single, simple PROM that could improve the consistency with which outcomes are reported. Originally derived from the Foot Function Index, the Ankle Osteoarthritis Scale (AOS) 3 is a disease- and region- specific instrument that covers 2 domains of measurement: Pain and Disability (Table 1). The AOS instrument was designed to measure the patient’s self-reported disability due to ankle arthritis in a manner that was accurate, brief, easy to administer, valid, and reliable. Research on the AOS by Pinsker et al 8 has demonstrated that the questions in the domains of pain and disability capture many key patient concerns both pre- and postoperatively during treatment for end-stage ankle arthritis. Understanding the way in which PROMs evaluate the treatment effect of surgery is warranted. The AOS records the patient’s responses to 18 separate items. For each item, scores increase as pain or impairment increases from “no pain” to “worst pain imaginable” along a 100-mm scale line. In each domain, the highest (ie, worst) score possible 714953FAI XX X 10.1177/1071100717714953Foot & Ankle InternationalWing et al research-article 2017 Measuring the Operative Treatment Effect in End-Stage Ankle Arthritis: Are We Asking the Right Questions? A COFAS Multicenter Study Kevin J. Wing, MD, FRCSC 1 , Nuria Chapinal, PhD 2 , Marcus P. Coe, MD, MS 3 , Timothy R. Daniels, MD, FRCSC 4 , Mark Glazebrook, MD, PhD, FRCSC 5 , Peter Dryden, MSc, MD, FRCSC 6 , Alastair Younger, MB/ChB, ChM, FRCSC 1 , Murray J. Penner, MD, FRCSC 1 , and Jason M. Sutherland, PhD 7 Abstract Background: Foot and ankle surgeons are increasingly relying on patient-reported outcome measures (PROMs) such as the Ankle Osteoarthritis Scale (AOS) to evaluate treatment options. The objectives of this retrospective cohort study were 2-fold: (1) to examine the AOS instrument using psychometric analysis and (2) to revise the questions on the AOS to improve the effect of questions on the score and remove redundancies. Methods: Pre- and postoperative patient scores were obtained from AOS questionnaires in the COFAS Prospective Ankle Reconstruction Database, a cohort of patients operatively treated for end-stage ankle arthritis. A split-sample approach was used to evaluate the AOS and to propose a revised instrument. Results: A total of 380 patients who had been treated with total ankle replacement or ankle arthrodesis were prospectively followed to the 2-year postoperative time point. Correlation analysis demonstrated that a number of questions on the AOS were highly correlated with other similar questions, frequently incomplete, or showed little variation between respondents. Eight of the original AOS questions were retained in the newly proposed Ankle Arthritis Score (AAS) [3 from the AOS Pain subscale and 5 from the AOS Disability subscale]. Principal components analysis (PCA) showed that these questions equally clustered into 2 domains in AAS: Basic Activity and Advanced Activity. Conclusions: The AAS is shorter and has improved psychometric properties as compared to the AOS. Further investigation is required to better characterize the clinical utility of this proposed new patient-reported outcome score. Level of Evidence: Level III, retrospective cohort study. Keywords: ankle arthritis, ankle arthrodesis, ankle replacement, patient-reported outcome measures (PROMs), Ankle Osteoarthritis Score (AOS), Psychometric analysis, Ankle Arthritis Score (AAS)