The Journal Of Bone And Joint Surgery - Volume 97 - Issue 10 - p. 818-823

Minimal Clinically Important Difference and the Effect of Clinical Variables on the Ankle Osteoarthritis Scale in Surgically Treated End-Stage Ankle Arthritis

Coe Marcus P., MD, MS; Sutherland Jason M., PhD; Penner Murray J., MD, FRCSC; Younger Alastair, MB, ChB, ChM, FRCSC; Wing Kevin J., MD, FRCSC
Ankle
Background: There is much debate regarding the best outcome tool for use in foot and ankle surgery, specifically in patients with ankle arthritis. The Ankle Osteoarthritis Scale (AOS) is a validated, disease-specific score. The goals of this study were to investigate the clinical performance of the AOS and to determine a minimal clinically important difference (MCID) for it, using a large cohort of 238 patients undergoing surgery for end-stage ankle arthritis.
Methods: Patients treated with total ankle arthroplasty or ankle arthrodesis were prospectively followed for a minimum of two years at a single site. Data on demographics, comorbidities, AOS score, Short Form-36 results, and the relationship between expectations and satisfaction were collected at baseline (preoperatively), at six and twelve months, and then yearly thereafter. A linear regression analysis examined the variables affecting the change in AOS scores between baseline and the two-year follow-up. An MCID in the AOS change score was then determined by employing an anchor question, which asked patients to rate their relief from symptoms after surgery.
Results: Surgical treatment of end-stage ankle arthritis resulted in a mean improvement (and standard deviation) of 31.2 ± 22.7 points in the AOS score two years after surgery. The MCID of the AOS change score was a mean of 28.0 ± 17.9 points. The change in AOS score was significantly affected by the preoperative AOS score, smoking, back pain, and age.
Conclusions: Patients undergoing arthroplasty or arthrodesis for end-stage ankle arthritis experienced a mean improvement in AOS score that was greater than the estimated MCID (31.2 versus 28.0 points).
Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Download article