Osteoarthritis and rheumatoid arthritis: Nursing pathophysiology

Osteoarthritis, or OA, and rheumatoid arthritis, or RA, are diseases that affect the synovial joints. OA is mostly a degenerative disease, while RA is a systemic autoimmune disease that can also impact other organs like the heart and lungs.

Joints, or the places where bones meet, can be classified into three main groups based on their structure and range of movement. Fibrous joints, like those between the bones of the skull in young children, are composed of a thin layer of fibrous tissue that allows for some movement to accommodate a child’s growing brain; by adulthood, the fibrous tissue is replaced by bone. On the other hand, cartilaginous joints, like the joints of the spine, contain a pad of fibrocartilage, allowing for some movement. Lastly, synovial or diarthrodial joints, like those of the wrist, shoulders, hips, and knees, are freely movable.

Okay, let’s take a closer look at synovial joints, which consist of two bones, each with its own layer of articular cartilage, a type of connective tissue that provides cushioning and allows the bones to glide against each other without friction. The cartilage has high tensile strength, which helps weight-bearing joints like the knees to distribute weight so the underlying bone absorbs the shock and weight. An important component of the articular cartilage are special cells called chondrocytes, which are essential for the maintenance and repair of the cartilage.

Surrounding the joint is an outer fibrous joint capsule that forms an inner space called the joint cavity, which is filled with synovial fluid. The inner surface of the joint capsule is lined with a synovial membrane, or synovium, which is mostly composed of connective tissue, elastic fibers, blood, and lymphatic vessels. It also contains macrophages that remove bacteria and debris, and fibroblasts that produce a viscous substance called hyaluronate, which is the main component of the synovial fluid, that lubricates the articular surfaces.

Now, OA is caused by damage to the synovial joints and can be categorized as primary or secondary. Primary, or idiopathic, OA occurs due to risk factors such as being biologically female; advanced age; obesity; joint trauma; and occupations that involve heavy lifting, prolonged standing, or repetitive motion. In contrast, secondary OA occurs when there’s a preexisting joint abnormality that can initiate biomechanical stress on the joint, like Marfan syndrome.