The disease has to do with the lubricating sac which sits in between major limb joints such as the ones in the knees and foot. It is a chronic disease and can even relust in the loss of function of the affected limb if not corrected. The areas between the joints of the bigger bones have a fluid sac (synovium) that contains synovial fluid that acts like the hydraulic fluid that fills shock absorbers on your car. This flud regulates and absorbs much of the forces that are excerted on the bones preventing them from contacting one another thus from damage. In rheumatoid arthritis, the synovial sac becomes inflammed and uncorrected can thin down so much it leaves the bones in contact with each other destroying the cartilage and bone in the process. The process of inflammation that is so characteristic of rheumatiod arthritis is not restricted to the bones but can also affect other organs in the human body.