What part of the bone is affected by arthritis?

Arthritis primarily affects the cartilage that lines the joints, which is the smooth tissue that enables bones to glide against each other. In osteoarthritis, the cartilage breaks down, leading to bone-on-bone friction, while in rheumatoid arthritis, inflammation occurs in the synovial membrane, which can damage both cartilage and bone. Over time, this can result in changes to the bone structure itself, such as bone spurs or erosion.