Validation of the Knee Injury and Osteoarthritis Outcome Score subscales for patients with articular cartilage lesions of the knee.

BACKGROUND The Knee Injury and Osteoarthritis Outcome Score (KOOS) assesses acute and chronic knee injuries or early-onset osteoarthritis in young, active patients. The United States Food and Drug Administration guidelines recommend that patient-reported outcome instruments used to support clinical trial label claims should demonstrate content validity using patient input and have acceptable psychometric properties in the target population. To use the KOOS subscales in safety and efficacy trials assessing new treatments for patients with articular cartilage lesions, additional validation work, using input from patients with articular cartilage lesions, was necessary. PURPOSE Qualitative and quantitative evaluations of the KOOS subscales' validity among patients with articular cartilage lesions were conducted to support their use as clinically meaningful end points in clinical trials. STUDY DESIGN Cohort study (diagnosis); Level of evidence, 2. METHODS For qualitative analysis, cognitive interviews involving concept elicitation and cognitive debriefing with the KOOS items were conducted with 15 participants aged 25 to 52 years. Participants either were candidates for cartilage repair or had undergone cartilage repair 6 months or more before the study. For the quantitative analysis, a psychometric evaluation of the KOOS was conducted with clinical trial data from 54 patients, aged 18 to 55 years, evaluating the Cartilage Autograft Implantation System in the United States (n = 29) and the European Union (n = 25). Data were collected before surgery and at 7 postsurgical visits up to 12 months. Internal consistency and test-retest reliability, construct validity, responsiveness, and estimates of the minimal detectable change (MDC) were assessed. Test-retest reliability was assessed using data from months 2 and 3 on a subset of stable patients. RESULTS Qualitative research confirmed that concepts measured on the KOOS are important to patients with articular cartilage lesions. Most participants reported the KOOS was comprehensive and appropriate. In the quantitative research, KOOS subscales showed excellent internal consistency reliability (range, .74-.97 at baseline) and test-retest reliability (range, .78-.82). Construct validity results supported hypothesized relationships, with significant correlations (r ≥ .50) in the expected directions. Responsiveness analyses demonstrated excellent sensitivity to change; standardized response means ranged from 0.8 to 1.2, and MDC estimates ranged from 7.4 to 12.1. CONCLUSION The study results support the use of the KOOS subscales among patients with articular cartilage lesions.