[en] Bony changes in forty-four knees of patients with clinically established rheumatoid arthritis (RA) were examined using magnetic resonance imaging (MRI) and plain film radiography. In all cases MRI was clearly superior to radiographs, demonstrating 25 marginal erosions and 42 subchondral cysts, while the number seen on radiographs was 3 and 8, respectively. These results emphasize the problems in visualizing bone erosions in large joints using plain films. MRI is the method of choice for detecting early changes in RA, not only because of its high sensitivity, but also because of the ability of contrast-enhanced MRI to provide physiological characterization of these lesions. (orig.)