This illustration shows the location of marginal erosions. They occur at the bare area of the joint, where the bone is not covered by articular cartilage within the joint capsule. These areas are often first to be eroded in inflammatory arthropathies.

In rheumatoid arthritis, the hypertrophic synovium and termed pannus destroy bone and cartilage within the joint. Although rheumatoid arthritis does not particularly follow a linear pattern, the bare areas usually erode first before the pannus erodes through the cartilage to the subchondral bone.