Clinical significance of meniscal damage on knee MRI.

What does this article say? Mark: This was a study of Framingham patients older than 50 years who were randomly selected to have magnetic resonance imaging (MRI) of their knees without regard to whether they had knee pain. Overall, 1,039 patients were screened, and of these, 991 had a readable MRI. All MRI films were read by one person with a background in orthopedics who looked exclusively at the right knee. If the reader wasn’t certain about the results, a musculoskeletal radiologist overread the film. Neither reader had knowledge of the patient’s clinical history (having or not having knee pain). This is important because if the readers know the patient’s clinical history ahead of time, they will often change their reading (review bias). Interobserver agreement (kappa) was 0.72. Plain radiography was also performed in 963 patients, and these films were read by a single musculoskeletal radiologist (kappa = 0.83). Kappa is a calculation of interobserver agreement beyond chance alone. For example, if two radiologists read the same film, what is the likelihood they will agree on the reading more than by chance alone? Kappa is usually scored as follows: 0 = no agreement; 0 to 0.2 = slight agreement; 0.2 to 0.4 = fair agreement; 0.4 to 0.6 = moderate agreement; 0.6 to 0.8 = substantial agreement; and 0.8 to 1 = almost perfect agreement. Bob: The use of kappa in this study is a bit strange. A second person read the MRI film only when the first reader wasn’t sure of the reading. Because the kappa measures agreement between the two readers, it would be tough to calculate a good kappa when one reader wasn’t committing to a diagnosis. Additionally, the only films read by the orthopedic radiologist were those that the first reader was unsure about. To calculate a valid kappa, both should have read all films. A better design would have been to have two readers look at each film independently. If they disagreed, a third reader could adjudicate. There is a second use of kappa in this study, with regard to the reading of the plain films (kappa = 0.83). Only one radiologist read the films, yet the study authors provide a kappa value. In this case, kappa is used to make the assumption that the reader had the same skills as readers in a previous study (the kappa of 0.83 must have come from prior studies, because only one person read the films in this study). This is an unorthodox use of kappa, and it lessens my confidence in the findings of this study. Mark: Thirty-five percent of patients (95% confidence interval, 32 to 38 percent) had meniscal damage, and 31 percent had a meniscal tear. Overall, 82 percent of patients with tibiofemoral osteoarthritis had coexisting meniscal damage. This went up to 95 percent in those with severe osteoarthritis. As expected, damage became more common with older age (more than 50 percent in persons 70 to 90 years of age). Importantly, 45 percent of those with meniscal tears and 25 percent of those without meniscal tears had “knee pain, aching, or stiffness on most days.” This means that most meniscal tears (55 percent) are asymptomatic. So, the finding of meniscal damage doesn’t automatically mean it is responsible for the patient’s pain.