Rheumatoid arthritis of knee joints: MRI-pathologic correlation

Objective: By comparing the MRI findings of menisci, articular cartilage, and subchondral bone marrow of knee joints with pathological characteristic in patients with rheumatoid arthritis (RA), to explore the MR characteristics and underlying mechanisms in RA knee joints. Methods: Between 2008 and 2014, 13 knee joints in 11 patients with RA, who had total knee arthroplasty, were included in the study, the degree of destructions of articular cartilage, bone marrow, menisci of knee joints were evaluated on MR images and pathological slices. When the pathologist was uncertain about the cell origin, the immunohistochemistry was done to identify the cell origin. We analyzed the degree of injury of articular cartilage and menisci,as well as the degree of injury of the pathological manifestations of subchondral bone, articular cartilage and menisci. We also compared the degree of pathological manifestations of the bone marrow edema under and distant from the bare area, using Mann-Whitney U test. Results: The articular cartilage destruction were level 4 and menisci damage were level 4 on MRI in most patients. Totally 52 locations presented bone marrow edema on MRI, 18 of 52 (34.6%) sites of bone marrow edema were covered by cartilage and distant from bare area, while 34 of 52 (65.4%) sites located under the bare area. Fibrosis, mosaic structure, and lymphocytes infiltration were the most common changes in bone marrow with edema. There was no significant difference in severity of pathological findings between the edema areas under and distant from areas with damaged articular cartilage. For articular cartilage damage, fibrosis and thinning of the cartilage, and cartilage hyperplasia were the most common pathological changes. 5 of 26 (19.2%) menisci were found in resected samples, all the menisci showed atrophy, thinning, and heterogeneous intensityon MR. Fibrosis, engulfing calcified debris and fibrinoid necrosis were most commonly seen in menisci samples. Conclusion: The menisci and articular cartilage are severely destroyed in patients with RA at late stage, bone marrow edema can be found at bare areas and areas distant from bare areas. RA in knee joints can involve several structures simultaneously, resulting in joint function decreased severely even disability. (authors)