Recently, I was given the opportunity to speak to members of the Arthritis Foundation about managing their activities when dealing with osteo- or rheumatoid arthritis. Many people either have osteoarthritis or rheumatoid arthritis or know someone who does. However, not all people understand the fundamental differences between these two types of arthritis. In osteoarthritis, the articular cartilage (the cartilage that lines the ends of your bones) starts to degenerate. The joint space becomes narrowed and bone spurs can form at the edges of the joint. Eventually, if enough degeneration occurs, there is injury to the bone lying underneath the cartilage and a person is told her joint is "bone on bone." In contrast, rheumatoid arthritis is an autoimmune disorder where the synovial tissue produces diseased and excessive synovial fluid. Normally, a person's synovial fluid gives proper nutrition to your cartilage and lubricates your joints but rheumatoid arthritis interrupts this process. This results in swollen, red and painful joints that can lead to deformities in the involved joint(s) if untreated. Osteoarthritis is more common in the weight-bearing joints, like your knees, hips and spine where rheumatoid arthritis typically involves the hands, feet or neck (but is not exclusive to these).