CHICAGO — The association between knee pain and the presence of pathologic features varies by the different compartments of the knee, Kathryn Wildy, M.D., reported at the 2004 World Congress on Osteoarthritis.
Using the Whole-Organ Magnetic Resonance Imaging Score (WORMS) system, a semiquantitative method that systematically scores 11 structural features, including articular cartilage, subarticular marrow edema, cysts, and bone attrition in eight different locations in the knee, Dr. Wildy and colleagues demonstrated how MRI studies that show the worst pathologically affected compartment, or even the total knee, often fail to correspond to the pain.
“When you look at the total knee, you probably are losing the story. We're looking at each compartment, rather than just the worst compartment, and you need to look at the different regions within each compartment,” Dr. Wildy said at the meeting sponsored by the Osteoarthritis Research Society International.
In their multicenter study involving 263 elderly men and women with discordant knee pain, axial, coronal, and sagittal plane studies were obtained on fast spin echo MRI and the WORMS system was used to score pathologic features of the knee. The patient's nonpainful knee served as a control.
Knee pain was defined as pain on most days of the month in the past year or moderate pain on the Western Ontario and McMaster University Osteoarthritis (WOMAC) index in the past 30 days; the mean WOMAC score was 6.2 for the painful knee and 0.4 for the nonpainful knee.
In this community-based population, the severity of cartilage damage, osteophytes, and synovitis were each independently associated with knee pain, reported Dr. Wildy, who led the study while at the University of Pittsburgh.
In the medial tibiofemoral compartment, bone attrition and bone marrow edema scores greater than 0 were significantly associated with knee pain; in the lateral tibiofemoral compartment the presence of all measured features was significantly associated with pain.
In the patellofemoral compartment, no feature was associated with pain. For the total knee, cartilage damage, bone attrition, and bone marrow edema scores greater than 0 were associated with knee pain, said Dr. Wildy, who now practices in Omaha, Neb.
Interaction between features revealed that bone marrow edema, which was common in the painful knees, was significantly associated with pain when accompanied by high cartilage damage in either the total knee (OR 3.27) or the medial tibiofemoral compartment (OR 2.0).