title: Minimal clinically important difference and the effect of clinical variables on the ankle osteoarthritis scale in surgically treated end-stage ankle arthritis.
abstract: 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).
authors.affiliation: Department of Orthopaedic Surgery, Dartmouth-Hitchcock Medical Center, One Medical Center Drive, Lebanon, NH 03756.
authors.forename: Marcus P
authors.initials: MP
authors.lastname: Coe
authors.affiliation: Centre for Health Services and Policy Research, School of Population and Public Health, University of British Columbia, 201-2206 East Mall, Vancouver, BC V6T 1Z3, Canada.
authors.forename: Jason M
authors.initials: JM
authors.lastname: Sutherland
authors.affiliation: Department of Orthopaedics, University of British Columbia, 1000-1200 Burrard Street, Vancouver, BC V6Z 2C7, Canada.
authors.forename: Murray J
authors.initials: MJ
authors.lastname: Penner
authors.affiliation: Department of Orthopedics, University of British Columbia, 560-1144 Burrard Street, Vancouver, BC V6Z 2A5, Canada.
authors.forename: Alastair
authors.initials: A
authors.lastname: Younger
authors.affiliation: Department of Orthopaedics, University of British Columbia, 1000-1200 Burrard Street, Vancouver, BC V6Z 2C7, Canada.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Wing
mesh_terms: D000368:Aged; D000843:Ankle Joint / Q000601:surgery; D058737:Arthroplasty, Replacement, Ankle; D001182:Arthroscopy; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000503:physiopathology / Q000601:surgery*; D011446:Prospective Studies; D016059:Range of Motion, Articular / Q000502:physiology; D012189:Retrospective Studies; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D016896:Treatment Outcome