Rheumatoid Arthritis: This is an autoimmune disease. In other words, this disease is triggered by abnormal functioning of the immune system. In this condition, the antibodies produced by the immune system start attacking the healthy tissues of the knuckle joints. As a result, the synovial membrane, which secretes the lubricating fluid called synovial fluid, suffers inflammation. The worst part of this disease is that it may lead to bone deformity.