Defining Responders vs Non-Responders After Total Ankle Arthroplasty

Abstract

Category: Ankle, Ankle Arthritis Introduction/Purpose: The literature for total ankle arthroplasty (TAA) demonstrates significant improvements in patient- reported outcomes. While these reports focus on the overall study population, it is clear that some patients do not have a successful outcome. In regards to total hip and knee arthroplasty there is literature helping to define responders, or those who achieve a clinical improvement above the level of a minimally clinically important difference. However, characteristics of responders versus non-responders to TAA have not been defined. The purpose of this study was to determine patient comorbidities and characteristics that help distinguish responders from non-responders after TAA. Methods: Patients undergoing TAA between 1/2007 and 12/2016 were enrolled into a prospective study at a single academic center. Patients completed multiple patient reported outcome measures before surgery and in follow-up including the Short Musculoskeletal Function Assessment (SMFA). Patients were characterized as responders if their 2-year follow-up SMFA function score increased by 50% or more compared to preoperatively and were characterized as non-responders if their SMFA score increased by less than 50% at 2-year follow-up, consistent with OMERACT–OARSI responder criteria. Patient and operative factors along with prevalent pre-operative comorbidities were then associated with responder or non-responder status. Comorbidities that met a significance threshold of p<0.05 in adjusted analyses were incorporated into multivariable outcome models. Results: A total of 492 patients with complete data and 2-year follow-up were included in this study. Based on the SMFA function score improvement cutoff of at least 50% at 2-year follow-up, 332 patients were defined as responders and 160 were defined as non-responders. There was no significant difference between pre-operative SMFA function scores between the groups. Responders had significantly higher preoperative SF-36 Mental Component Summary (MCS) scores (p<0.001) and significantly lower rates of rheumatoid arthritis (p<0.001), obesity (p=0.05) and depression (p=0.026) as compared to non-responders. In multivariate analysis, preoperative SF-36 MCS score was found to be significantly associated with responder status (p=0.0056). Conclusion: Patients defined as responders after TAA based on 50% or greater improvement in SMFA function scores at 2-year follow-up had significantly higher pre-operative SF-36 MCS scores and significantly lower rates of rheumatoid arthritis, obesity and depression compared to non-responders. Pre-operative SF-36 MCS score was found to be significantly associated with responder status in multivariate analysis. This suggests that patients with depressive symptoms, but not necessarily a diagnosis of depression may not achieve as favorable results after TAA and should be counseled appropriately.