Rigorous statistical reliability, validity, and responsiveness testing of the Cincinnati knee rating system in 350 subjects with uninjured, injured, or anterior cruciate ligament-reconstructed knees

Although many instruments are used to assess outcome after knee ligament re construction, their reliability, validity, and responsiveness have not been adequately proven. Our purpose was to assess these statistical measures in a commonly used instrument, the Cincinnati Knee Rating System. Reliability was determined from the responses of 100 subjects who completed the instru ment twice, a mean of 7 days apart. Validity and responsiveness were assess ed from 250 patients observed for at least 2 years after autogenous ACL rec onstruction. Questionnaire items included symptoms, functional limitations with sports and daily activities, patient perception of the knee condition, and sports- and occupational-activity levels. The items demonstrated high test-retest reliability, supporting their use in evaluating groups of patie nts between two different treatment periods (all intraclass correlation coe fficients >0.70). In addition, the questionnaire demonstrated good content validity, construct validity, and item-discriminant validity. For the overa ll rating score, no "floor effects" (worst score possible) were found befor e or after surgery. No "ceiling effects" (best score possible) were found b efore surgery, and, at follow-up, these effects were calculated in only 22 patients (9%). The questions were found to be highly responsive to detectin g changes between evaluations. The data demonstrated that this rating syste m has acceptable reliability, validity, and responsiveness for use in outco me studies after knee ligament reconstruction.