Reproducibility and Reliability of the Outerbridge Classification for Grading Chondral Lesions of the Knee Arthroscopically

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Abstract
Background: Few studies have investigated the accuracy and reproducibility of the Outerbridge classification system for classification of chondral damage in the knee. Hypothesis: Arthroscopically assigned Outerbridge grades are accurate, reliable, and reproducible. Study Design: Cadaver study. Methods: Six cadaveric knees underwent diagnostic arthroscopy, which was videotaped. An arthrotomy was then performed and the arthroscopically identified lesions were measured with calipers. Nine orthopaedic surgeons reviewed each video and graded each chondral lesion two separate times. Accuracy of observations was calculated based on the percentage of agreement between the grades determined during arthroscopy and arthrotomy. Results: The overall accuracy was 68% but varied by location. The kappa coefficient between the two scores was 0.602; the arthroscopy grade was higher than the arthrotomy grade 63% of the time. The intraobserver and interobserver kappa coefficients were 0.80 and 0.52, respectively. The mean interobserver kappa between the two physicians in practice 5 years or more was 0.72, compared with 0.50 for physicians in practice less than 5 years. Conclusions: The Outerbridge classification was moderately accurate when used to grade chondral lesions arthroscopically. Clinical Relevance: Orthopaedic surgeons can accurately grade chondral lesions of the knee with the Outerbridge classification, regardless of their level of experience.

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