The Synovium, Synovitis, Inflammation, and Joint Pain
The Synovium and Synovitis
The synovium is a membrane that lines the inside of many of our joints. It secretes a lubricating fluid that helps a joint to function properly. Unfortunately, the synovium may sometimes become inflamed, resulting in a painful condition called synovitis. Synovitis often occurs as a symptom of rheumatoid arthritis, lupus, or gout. It may also be present due to an infection or an injury in the joint.
For a long time it was thought that no inflammation—and therefore no synovitis—was present in the joints of someone suffering from osteoarthritis. Now researchers are discovering that inflammation is involved in at least some cases of osteoarthritis and that synovitis may be present.
Ligaments joins bones together at a joint. A tendon attaches a muscle to a bone. A bursa is a sac that is lined by synovial membrane and filled with fluid. It acts as a cushion between a bone and a tendon or a muscle.
What Is a Synovial Joint?
A joint in the human body is a region where one bone ends and another begins. The most common type of joint in our body is called a synovial joint. In this type of joint, there is a small space between the ends of the bones. The space is known as the synovial cavity. The surfaces of the bones are covered with a thin layer of articular cartilage and the joint is surrounded by a capsule. The inner lining of this capsule is the synovium, or synovial membrane. Synovial joints are present in the limbs, shoulders, and hips and between the first and second cervical vertebrae in the neck.
Types of Synovial Joints
Functions of the Synovium
The synovium secretes a lubricating fluid into the space between the bones. This fluid is known as synovial fluid. The fluid and the articular cartilage work together to reduce friction, absorb shock, and ensure that the bones move smoothly over each other as a person moves his or her body.
Synovial fluid is clear, colorless, and thick. It resembles uncooked egg white in appearance. The fluid's name is derived from "ovum", the Latin word for egg. It contains water, enzymes, and other substances, including hyaluronate (or hyaluronic acid) and a protein called lubricin. Hyaluronate and lubricin work together to lubricate the surfaces of the bones. Synovial fluid also transfers nutrients from the blood to the articular cartilage.
Inflammation or the Inflammatory Response
In synovitis, the synovium is irritated by a trigger of some kind and becomes inflamed. During this inflammation, the synovium becomes thickened and filled with fluid. Some of the fluid escapes into the joint capsule. This makes the joint swollen and painful, which in turn makes movement of the joint difficult.
Unfortunately, a cascade of damaging events takes place when the synovium is irritated. In this cascade, there is an increased blood flow to the joint, which may make the area feel warm. White blood cells leave the blood and enter the joint capsule. Here they release inflammatory chemicals. As a result, the articular cartilage may be damaged.
Temporary inflammation is generally beneficial because it helps an injury to heal. Chronic or excessive inflammation is harmful and can damage body structures.
Synovitis and Cartilage Destruction in Rheumatoid Arthritis
Synovitis in Rheumatoid Arthritis, Lupus, and Gout
Synovitis is a major symptom of several diseases. Rheumatoid arthritis is an autoimmune and inflammatory condition in which a person's immune system mistakenly attacks the synovium of the joints. The synovium becomes inflamed and the joint becomes swollen, painful, and stiff. Eventually, the joint is damaged by the inflammation. Other areas of the body may also become inflamed in a person suffering from rheumatoid arthritis.
Like rheumatoid arthritis, lupus (systemic lupus erythematosus, or SLE) is an autoimmune problem. The body attacks healthy body tissue, such as the synovium. Although lupus can be a serious condition and can cause problems in several parts of the body, the swelling in a joint and the joint damage are generally less severe than in rheumatoid arthritis.
In gout, a substance called uric acid builds up in the blood. There are many possible causes of an increased uric acid level. They include dietary factors, obesity, certain medical conditions and medications, genetics, and age.
Excess uric acid is deposited as crystals in joints and sometimes in other body parts as well. The crystals cause the synovium to become inflamed. Gout often develops in the big toe, resulting in swelling, redness, warmth, and severe pain.
Men generally have a higher uric acid level and are more likely to develop gout than women. After menopause, however, a woman's uric acid level begins to rise and she becomes more susceptible to developing gout.
Synovitis of the Shoulder
Transient or Toxic Synovitis
Transient synovitis is a temporary condition that is also called toxic synovitis. It causes hip pain and limping in young children. The disorder is more common in boys than girls. Generally one hip is affected, but the pain may start in one hip and then move over to the other one. The problem is thought to be caused by a viral infection that triggers inflammation of the synovium in the hip joint. The affected child usually has a mild fever. The virus may cause other symptoms, such as a cold or stomach flu.
Transient synovitis is unpleasant for the child and can be worrying for the parents, but in general it isn't a serious condition. It's often treated with anti-inflammatory drugs, pain medications, and rest. It's usually gone in one or two weeks, although it can last for a month or more. Some unlucky children have a tendency to develop transient synovitis whenever they have a cold or another viral infection.
Transient synovitis doesn't cause permanent joint damage. However, it's very important to see a doctor to get a correct diagnosis because the symptoms may indicate a more serious problem called septic arthritis. This is caused by a bacterium instead of a virus and can result in long-term joint damage.
Transitory synovitis is almost always restricted to children up to the age of ten. There have been a few reports of the disease appearing in adults, however.
Transient Synovitis in the Hip
Pigmented Villonodular Synovitis
Pigmented villonodular synovitis (PVNS) usually affects the knee or the hip, but it may develop in other joints instead. In PVNS, the synovium grows and becoming larger than normal. It may also form folds (villi). The condition is sometimes referred to as a benign tumor. A benign tumor isn't cancerous and doesn't spread through the body. PVNS is generally progressive, however, and gradually becomes worse.
In PVNS, the entire synovium may be enlarged (diffuse PVNS), or the enlargement may be in only one place (localized PVNS). Sometime enlarged tissue forms a nodule that is attached to the synovium by a stalk. Another feature of the condition is the buildup of a chemical called hemosiderin in the synovium. Hemosiderin contains iron and is yellow-brown in color.
The main symptoms of PVNS are pain and swelling in the joint. The swelling is sometimes impressive. A patient may also discover that the affected joint locks. Unfortunately, the cause of pigmented villonodular synovitis is currently unknown. In some people, it develops after an injury to the joint.
Anyone with continuous or repeated joint pain should visit a doctor for a diagnosis and treatment recommendations. The treatments described below are mentioned for general interest only.
A person with synovitis should be under a doctor's care. The first line of treatment is often the use of anti-inflammatory drugs. These may be NSAIDs (nonsteroidal anti-inflammatory drugs) such as aspirin or ibuprofen, or more powerful corticosteroids, which may be given in the form of cortisone injections. Specialized medications like antirheumatic drugs may also be prescribed.
If synovitis lasts for a long time and doesn't respond to other treatments, a synovectomy may be performed to provide relief. This is either a partial synovectomy (removal of part of the synovium) or a total synovectomy (removal of the entire synovium), using surgery, injection of a radioactive isotope into the joint, or the application of chemicals that destroy the synovium.
The synovium is very useful when it's functioning properly. When it's damaged, however, it can cause a lot of pain. Medical treatments for synovitis can be very helpful. Some cases may be more challenging to treat than others, though. Hopefully new and improved treatments will soon be available.
© 2012 Linda Crampton