Osteoarthritis and Inflammation - Exploring the Connection
The Nature of the Disease
Osteoarthritis is a disorder in which the cartilage in a joint degenerates and eventually disappears. The cartilage normally covers the ends of the bones in a joint and acts as a low-friction cushion between them as the bones move. When the cartilage is absent, the end of one bone rubs against the end of another, causing pain and difficulty in movement. Osteoarthritis is often a symptom of aging, but it may appear at any age due to an injury to a joint.
It was once thought that osteoarthritis was caused solely by wear and tear and involved no inflammation, unlike rheumatoid arthritis. The latter disorder is an autoimmune and inflammatory condition that affects joints and other parts of the body as well. Now researchers know that inflammation is also involved in osteoarthritis. It may not be as severe as that found in rheumatoid arthritis, but it may still be be significant.
Differences Between Osteoarthritis and Rheumatoid Arthritis
Who Gets Osteoarthritis?
Osteoarthritis is the most common form of arthritis. It's also known as degenerative arthritis or degenerative joint disease. Its name is sometimes abbreviated as OA. OA can affect any joint in the body, but it most commonly appears in joints located in the spine, hips, knees, feet or hands.
Research indicates that the majority of people in North America will have some degree of osteoarthritis by the time they are seventy. Not everyone will experience symptoms of the disorder. For some people, however, osteoarthritis is a painful disease. It may also be disabling.
A Synovial Joint
The synovial joint is the most common type of joint in our body and is the site of osteoarthritis development.
What Happens to a Joint in OA?
A joint is a region where two bones meet. The type of cartilage that covers the ends of the bones is known as hyaline cartilage. It's a stiff but flexible material that is very slippery and allows bones to move over each other smoothly with low friction. If this cartilage gradually disappears, as it does in osteoarthritis, the ends of the bones will rub together.
The cartilage in a joint is sometimes known as articular cartilage. The body may form extra bone in a joint that lacks this cartilage. The extra bone forms irregular projections called bone spurs or osteophytes. Pieces of bone spurs may break off and be trapped in the joint, along with broken bits of cartilage. It's generally thought that these bits of bone and cartilage irritate the membrane that lines the joint capsule, causing inflammation, although there are additional theories to explain why the joint lining becomes inflamed.
A Doctor Describes Osteoarthritis
Symptoms of OA
There may be no symptoms of osteoarthritis. Some people experience problems, however, which may be severe.
- A person with OA may experience pain when moving the affected joint or when putting weight on it.
- The joint may be stiff, especially after a person wakes up or after they have been inactive for a while.
- There may be limitation in movement. The presence of osteophytes may further limit movement.
- Bone spurs in a joint may produce a knobby appearance.
- There may be a creaking, crackling or grating sound or sensation when the joint is moved. This sound is known as crepitation or crepitus.
Although there are treatments to make osteoarthritis more bearable, there is no cure for the disease, other than replacing the diseased joint with an artificial joint. Therefore researchers are very interested in finding ways to stop the progression of OA.
Types of Inflammation
Acute inflammation appears rapidly and lasts for a short period of time. It's a normal body response to an infection or an injury and is usually a beneficial process in our bodies. During acute inflammation, there is increased blood flow to the injured area. The blood carries white blood cells and proteins to fight bacteria and remove damaged tissue cells. The blood vessels become more permeable, allowing the beneficial substances to leave the blood and enter the injured tissue. Possible signs and symptoms of acute inflammation are heat, swelling, redness and pain.
Chronic inflammation lasts for a long time. It may be weaker than acute inflammation. Sometimes acute inflammation becomes chronic instead of being resolved, however. In chronic inflammation, the concentrations of white blood cells and of proteins associated with the inflammation remain abnormally high and can damage tissues. This can lead to health problems. Both acute and chronic inflammation may be involved in osteoarthritis.
Inflammation in Osteoarthritis
Inflammation is being found in osteoarthritic joints with increasing frequency. The inflammation arises from damage to the synovium that lines the inside of a joint capsule. Some researchers have proposed that the inflammation in the synovium is being caused by inflammation in an enthesis, which is the place where a ligament or a tendon joins to bone.
Ligaments are fibrous structures that join one bone to another at a joint. Tendons are fibrous structures that join muscles to bones at a joint.
What Causes the Joint Inflammation?
The synovium is also known as the synovial membrane or the synovial lining. It covers the inside of the capsule surrounding a joint and produces synovial fluid, which nourishes the articular cartilage.
Inflammation of the synovium is called synovitis. In osteoarthritis, the inflammation is thought to appear when broken pieces of articular cartilage - and broken pieces of bone spurs, if they form - irritate the synovium. However, this doesn't explain all cases of osteoarthritis inflammation. Researchers have been puzzled by the fact that in some cases of early osteoarthrotis, synovitis has existed without cartilage breakdown and without bone spur formation.
Ligaments join bones together and tendons attach muscles to bones. The entheses are transition areas where ligaments and tendons join to a bone: they contain collagen fibers like the ligaments and tendons but also contain minerals like bone.
Some UK scientists have found evidence that an inflamed enthesis influences the synovium in a joint and causes it to become inflamed, too. Once the synovium is inflamed the articular cartilage begins to degenerate. According to this idea, the inflammation of the synovium is the cause of osteoarthritis instead of the result.
Impact of OA
The Significance of the Complement System
There is additional evidence that inflammation may be a cause of osteoarthritis instead of (or as well as) a result of the disease. A research team at Stanford University in the United States has shown that osteoarthritis may develop due to a malfunctioning complement system.
The complement system is part of the immune system. It's normally activated to help other components of the immune system fight infectious bacteria and viruses that have entered the body. It "complements" the action of the rest of the immune system.
The complement system consists of proteins which take part in a series of reactions known as the complement cascade. The process ends with the activation of a special complex of proteins called the membrane attack complex. This complex kills cells by creating holes in their membranes. This is very useful if a cell that is being attacked is a bacterial cell.
Although the complement system is helpful in the fight against harmful microbes, it's dangerous for healthy cells, since its function is to destroy cells. Therefore the body makes control proteins that act as brakes for the complement cascade.
The Complement System in Osteoarthritis
The research carried out by the Stanford scientists suggests that the first step in the development of osteoarthritis is damage to a joint. As a result of the damage, the complement system is activated.
By extracting and analyzing joint fluid from people with and without osteoarthritis, researchers have found that people with osteoarthritis have an excessive number of proteins that accelerate the complement cascade and a low level of the proteins that stop the cascade compared to the levels in people without osteoarthritis. The researchers believe that in susceptible people the complement system attacks the injured joint, causing inflammation and damage to the articular cartilage.
Reducing the Risk of Osteoarthritis
Tips for Preventing or Delaying Osteoarthritis
Since osteoarthritis often develops due to an injury to a joint, it's very important to try to reduce injuries and to treat them properly if they do happen. Joint degeneration may not be noticed until years after an injury. Although there does seem to be an inherited tendency to develop osteoarthritis in some people, everybody can reduce their risk of joint degeneration by taking some precautions. Here are some tips.
- It's known that weight gain increases the risk of hip and knee arthritis, since there is increased force exerted on the lower body joints as the person moves. Maintain a healthy weight to reduce the chance of osteoarthritis developing.
- Exercise to strengthen the muscles around the joint to reduce the chance of injury.
- Avoid repetitive exercise that stresses a joint.
- Maintain good posture to protect certain joints from pressure.
- Do warm-ups before participating in sports.
- Participate in a variety of exercise activities that emphasize the use of different muscles and joints.
- Start a new physical activity carefully, gradually increasing the intensity.
- Wear safety equipment if necessary during an activity, such as knee pads for inline skating.
- Use proper body mechanics when lifting weights to avoid injury
- If you are injured, get proper treatment and wait for the injury to heal completely before returning to the activity that caused the injury.
Do You Have Arthritis?
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Some Ways to Relieve Osteoarthritis Pain
Treatments for OA
At the moment, the main treatment for osteoarthritis is the use of pain relievers and anti-inflammatory medications such as acetaminophen (paracetamol) or ibuprofen. These can help remove pain for a while but don't stop the progression of the disease. There are also creams available that relieve pain temporarily when placed on a joint. Some people find that the application of cold or heat makes their sore joints feel better. Doctors may prescribe more powerful medicines than over-the-counter medications. They may also inject potentially helpful substances into a joint, such as corticosteroids or hyaluronic acid.
Physical therapy may be helpful for osteoarthritis in some parts of the body, and so may specific joint exercises. These exercises must be done with medical advice, however, in order to improve the function of the joint instead of making it worse.
The Stanford University researchers hope to find ways to stop the complement cascade in joints in order to end inflammation. This may be tricky, however, because anything that stops the complement cascade in our body may also increase our susceptibility to bacterial and viral infections. If researchers can find a way`to hinder the complement system only in damaged joints and nowhere else in the body they may have an effective way to prevent osteoarthritis, or at least to slow its progression.
Since the incidence of osteoarthritis seems to be increasing in many countries, researchers are trying to understand the disease better in order to find improved treatments. Hopefully these improved treatments will appear very soon.
References and Further Reading
General Osteoarthritis Information from the NIH (National Institutes of Health)
Inflammation of the Enthesis and its Role in Arthritis from Arthritis Research UK
The Complement System and Osteoarthritis from Stanford University
Sokolove J, Lepus CM. Role of inflammation in the pathogenesis of osteoarthritis: latest findings and interpretations. Therapeutic Advances in Musculoskeletal Disease . 2013;5(2):77-94. doi:10.1177/1759720X12467868.
© 2012 Linda Crampton
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