Reliability and validity of 6 measures of pain, function, and disability for ankle arthroplasty and arthrodesis

Background: Patient-reported outcome measures are increasingly used evaluating clinical care. Many measures used to assess operative hindfoot interventions vary in content, and some have not been psychometrically validated in this population. The purpose of this study was to compare measurement properties of 6 lower-extremity patient-reported outcome measures, and to evaluate their reliability and validity in light of patients' preferences.

Methods: Cross-sectional survey of 42 preoperative and 100 postoperative patients completed 6 lower-extremity outcome measures on 2 occasions: Foot Function Index (FFI), Ankle Osteoarthritis Scale (AOS), patient-reported items of the American Orthopaedic Foot & Ankle Society Questionnaire (AOFAS), Lower Extremity Functional Scale (LEFS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and the Short Musculoskeletal Function Assessment (SMFA), as well as measures of preference, and symptoms.

Results: Internal consistency was good to excellent for all scales and subscales (α = .84-.97; ICC [2,1] = .81-.96). Correlations between scales ranged from .50 (WOMAC(Stiffness) and FFI(Activity) Limitations) to .92 (LEFS and SMFA(Overall), WOMAC(Pain) and AOS(Overall), FFI(Overall) and AOFAS(Overall)). Higher correlations occurred within instruments (r = .97 AOS(Pain) and AOS(Overall)) and between similar subscales from different instruments (r = .91 WOMAC(Pain) and AOS(Pain)). Construct validity showed moderate to high correlations to global ratings of Pain, Stiffness, and difficulty performing Daily Activities. The highest correlations (r > .75) occurred between Pain and AOS(Overall) (r = .84), stiffness and WOMAC(Stiffness) (r = .81), and Daily Activities and AOS(Disability) (r = .87). Patients rated instruments by preference. FFI, WOMAC, LEFS, and SMFA rated favorably for length. FFI, WOMAC, LEFS, and AOFAS rated high for understandability. FFI was rated by postoperative patients as most likely to capture change due to surgery. SMFA rated the best overall.

Conclusions: Direct comparison of instruments revealed similarity between scales in construct validity and reliability. Patient preferences supported the use of these scales. Foot-specific instruments offered no clear advantage over lower-extremity instruments.

Level of evidence: Level II, prospective comparative study.