title: The use of the Core Outcome Measures Index (COMI) in patients undergoing total knee replacement.
abstract: BACKGROUND
  The Core Outcome Measure Index (COMI) is a very short outcome instrument used in spine patients. The aim of this study was to examine the utility of a knee version of the COMI in patients undergoing total knee arthroplasty (TKA) by assessing the reproducibility, construct and discriminant validity, and responsiveness.
  
  
  METHODS
  Preoperatively, 224 patients completed the Oxford Knee Score (OKS), EuroQoL (EQ-5D) and the COMI-Knee; 189 (84) % also completed the questionnaires at follow-up and 73 patients completed preoperatively the COMI-knee twice.
  
  
  RESULTS
  The weighted kappa values for the COMI-knee single items ranged from 0.80 to 0.89 and the ICC for the COMI-knee (composite score), 0.86. The absolute SEM for COMI-knee was 0.4 points, i.e. four percent of the maximum value (10 points) and six percent of the average value (6.6 points). The Area Under the Curve derived from the Receiver Operating Characteristic method for the COMI-knee was 0.97 (95% CI, 0.93 to 0.99), with a cut-off value for indicating a "good" result of 2.3 (100% specificity, 87% sensitivity). Correlations between the COMI-knee and the OKS were -0.72 at baseline and -0.87 at six months. The correlations between the change scores for the COMI-knee and the change scores for the OKS and EQ5D index were 0.77 and 0.69, respectively.
  
  
  CONCLUSIONS
  The measurement properties of the COMI-knee satisfy international quality criteria and hence support its use in assessing patients undergoing TKA.
authors.affiliation: Research & Development Department, Schulthess Clinic, Lengghalde 2, 8008 Zurich, Switzerland. Electronic address: franco.impellizzeri@gmail.com.
authors.forename: Franco M
authors.initials: FM
authors.lastname: Impellizzeri
authors.affiliation: Department of Orthopaedic Surgery, Schulthess Clinic, Lengghalde 2, 8008 Zurich, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Leunig
authors.affiliation: Department of Orthopaedic Surgery, Schulthess Clinic, Lengghalde 2, 8008 Zurich, Switzerland.
authors.forename: Stefan
authors.initials: S
authors.lastname: Preiss
authors.affiliation: Department of Orthopaedic Surgery, Schulthess Clinic, Lengghalde 2, 8008 Zurich, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Guggi
authors.affiliation: Research & Development Department, Schulthess Clinic, Lengghalde 2, 8008 Zurich, Switzerland.
authors.forename: Anne F
authors.initials: AF
authors.lastname: Mannion
mesh_terms: D019645:Arthroplasty, Replacement, Knee; D004185:Disability Evaluation; D006801:Humans; D000071066:Patient Reported Outcome Measures; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires
keywords: Clinimetrics; Core set; Instrument; Knee arthroplasty; Psychometrics; Questionnaire