The reliability of the American Knee Society Score.

We have investigated the reliability of the American Knee Society Score (AKS), a widely used functional outcome score for knee arthroplasty. 29 subjects were assessed in random order by 6 observers, each patient seen twice by each observer. The interobserver reference intervals were 16 points for the Knee Score (0-100 points) and 21 points for the Function Score (0-100 points). The intraobserver reference intervals were smaller, 11 points and 13 points for the Knee Score and the Function Score, respectively. The presence of arthritis in other joints and general debility did not affect the reliability of the scores. The more experienced observers had greater intraobserver reproducibility. Notably, we found moderate agreement between observers in the subjective variables, while the objective variables produced lower levels of agreement. The high inter- and intraobserver variations of the AKS makes estimation of score change questionable. Reliable use of the AKS would necessitate repeated evaluation by an experienced observer.