Effect of Patient Demographics on Minimally Important Difference of Ankle Osteoarthritis Scale Among End-Stage Ankle Arthritis Patients

Abstract

Background: Ankle replacement and ankle arthrodesis are standard treatments for treating end-stage ankle arthritis when conservative treatment fails. Comparing patient-reported outcome scores to the instrument’s minimal important difference (MID) helps physicians and researchers infer whether a meaningful change in health from the patient’s perspective has occurred following treatment. The objective of this study was to estimate the MID of the Ankle Osteoarthritis Scale among a cohort of operatively treated end-stage ankle arthritis patients undergoing ankle replacement or arthrodesis. Methods: A survey package including the Ankle Osteoarthritis Scale was completed by participants preoperatively and 2 years postoperatively. Distribution and anchor-based approaches to calculating the MID were used to estimate the MID of the Ankle Osteoarthritis Scale and its 2 domains. The distribution-based approaches used were the small and medium effect size methods, while the mean absolute change method and linear regression method were the anchor-based approaches. Bootstrap sampling was used to obtain the variance of MID estimates. The MID was estimated for sex, age, operative, and baseline health subgroups. The cohort comprised 283 participants, totaling 298 ankles. Results: The MID did not vary with sex or operative procedure. Age-based differences in MID values may exist for the Ankle Osteoarthritis Scale total score, and MID values were generally smallest among the oldest patients. Patients with the best and worst ankle-related health preoperatively had higher MID values than patients reporting mid-range Ankle Osteoarthritis Scale values preoperatively. Conclusions: The best estimate of the MID of the Ankle Osteoarthritis Scale total score is 5.81. Our findings indicate that the MID of the Ankle Osteoarthritis Scale may not vary by sex or operative subgroups but likely varies by age and preoperative Ankle Osteoarthritis Scale score. Level of Evidence: Level II, prospective comparative study.

Sex Differences in End-Stage Ankle Arthritis and Following Total Ankle Replacement or Ankle Arthrodesis

“…The MCID of the AOS pain and disability scales was previously established to be approximately 28 points at 2 years of follow-up 33 and 12.4 points at 5 years of follow-up 34 . A recent study utilizing both distribution and anchor-based approaches determined a best estimate MCID of 5.8 points for the AOS total score 35 . The MCID did not vary by sex or surgical procedure, but varied by age and preoperative AOS score 35 .…”

“…A recent study utilizing both distribution and anchor-based approaches determined a best estimate MCID of 5.8 points for the AOS total score 35 . The MCID did not vary by sex or surgical procedure, but varied by age and preoperative AOS score 35 . This finding suggests that the significant sex-related differences that we observed in our study are likely not clinically meaningful.…”

“…The AOS, a disease and joint-specific outcome score, measures pain and disability related to ankle arthritis 30 and has demonstrated internal consistency, test-retest reliability, and construct validity for end-stage ankle arthritis, total ankle replacement, and ankle arthrodesis 31,32 . The minimum clinically important difference (MCID) of the AOS lies between 5.8 and 28 points [33][34][35] . Lower scores indicate less pain and disability.…”

What’s New in Foot and Ankle Surgery

“…There is a growing recognition that many of the commonly used scales may not be fully linear and that their properties may vary in different patient populations. Sutherland et al 2 used distribution and anchor methods to determine the minimally important difference for the Ankle Osteoarthritis Scale in a large cohort of 283 patients. The minimally important difference was shown to be smaller for older patients.…”

Validation of the Foot and Ankle Outcome Score (FAOS) for Osteochondral Lesions of the Ankle

“…9 Additionally, a limitation of the AOFAS score compared to the FAOS is its variation in minimally clinically important difference among different patient cohorts. 23 Conversely, a major shortcoming of the FAOS is its inherent time-intensive nature. Despite the substantial benefits provided by the FAOS, the FAOS was ranked 11th in a list of the most commonly used outcome tools in foot and ankle literature over the last decade.…”