In rheumatoid arthritis, synovial inflammation and synovial hyperplasia make the synovium invade and eat into the cartilage and bone at the joints. On an x-ray, the bones can be seen to have damaged areas caused by this invasion, and they look like little bites out of the corners of the bones. These are called erosions. Sometimes this term is used for other forms of imaging, such as MRI scans, but this is a much less precise use. Sometimes ‘erosions’ is used to describe any little bite out of a bone seen on an x-ray in any condition, but this also is a much less precise use.