The most basic definition of arthritis is the inflammation of a joint.
A common misunderstanding that patients have is the difference between the various types of arthritis. They are often concerned that a family member had “crippling arthritis” or “rheumatism” and that they will develop the same disease. Even normal aches and pains cause anxiety.
The most basic definition of arthritis is the inflammation of a joint. Most people have a good idea of what a joint is—the location where two bones come together and move such as the knee or hip. Other joints that don’t move, called fixed joints, are less understood. An example of a fixed joint is where the pelvic bones connect to each other or the ribs meet the breastbone.
All types of joints contain a smooth material, called cartilage, which covers the ends of the bones. Cartilage provides low friction gliding and cushioning between the bones. A different type of cartilage, called meniscal cartilage, helps to stabilize the joint. In addition, two separate layers of tissue surround every joint. The outer layer, called the capsule, is a tough thick material that also helps to stabilize the joint. An inner layer, called the synovium, secretes joint fluid to lubricate the movement of the joint.
Ligaments are extremely tough bands of tissue that surround and stabilize joints. Tendons attach the muscles to the bones and power the joints.
Any failed component of the joint can produce arthritis. For example, bacteria in the joint fluid is called septic arthritis. Although the process starts in the fluid component, it quickly involves the other parts of the joint. Other types of arthritis are crystalline deposition disease and seronegative arthritis.
The two most common types of arthritis are osteoarthritis and rheumatoid arthritis. Osteoarthritis, or OA, is the classic wear and tear arthritis that affects mostly the cartilage portion of a joint. Anything that mechanically affects the joint surface can cause it to wear away leaving raw bone exposed. A classic analogy is the tread on a tire. A tire can wear out after many years from the gradual abrasion of the road, or it can also fail after going through a pothole. In much the same way, an individual’s joint can degrade over decades of use or it can have accelerated changes that occur quickly, such as after a fracture.
The effects of OA are most noticeable in weight bearing joints with pain most often noticed when the joints are in use during weight bearing and is less symptomatic at rest. Once the cartilage wears away, the body’s response is predictable and includes the formation of bone spurs to create more surface area to distribute joint forces.
Sclerosis or hardening of the joint is due to increased stress on the joint. Cyst formation is due to cracks or small fractures that allow synovial fluid to create caverns or cysts in the bone. These activities are obvious on a physical exam and are easily seen on a plain radiograph. Once the changes of OA begin, they are usually progressive although various interventions can slow the progress of the disease.
Treatment of OA aims to correct the mechanical issues in the joint. Anything that keeps the bones from rubbing together helps to lessen the pain. Orthopedists use various techniques to treat including injection of fluid to cushion the joint, surgical removal of bone and cartilage fragments, the mechanical realignment of joints, and the resurfacing or replacement of worn out cartilage.
Rheumatoid arthritis, or RA, differs from OA in several key ways. RA is a disorder of the immune system whereby the body produces substances that actually attack different structures in the body. Unfortunately, the lining or synovium of a joint is one of the most common tissues attacked. Instability of the joint and secondary changes in the cartilage follows. On examination, joints are often warm, swollen and tender with the joint often painful even at rest. Since the immune system is involved, many joints are involved at the same time. RA is more common in women and often diagnosed at a younger age than OA. RA has fewer findings on radiographs, but is diagnosed and monitored by various laboratory tests that measure the function of the immune system.
The goal of RA treatment is to keep the body from attacking itself while still allowing it to protect itself from outside threats. Often, powerful drugs similar to the medicines used to treat cancer are used to control an overactive immune system. Locally active drugs such as cortisone can be injected directly into a joint to control the inflammation and swelling. When all else fails, the joint surfaces that have been destroyed have to be replaced surgically.
While common forms of arthritis are not curable, with accurate diagnosis and early treatment most symptomatic joints can remain functional and pain free for a long time.