Arthritis
Arthritis is an inflammatory joint disease that can damage the joints of the body. It is to be distinguished from osteoarthritis, which is a degenerative condition related to aging and wear and tear of cartilage. While osteoarthritis is a cold process involving gradual deterioration, other forms of arthritis are characterized by redness, swelling, warmth and the abnormal collection of joint fluid known as joint effusion.The term monoarticular arthritis refers to arthritis in a single joint and polyarticular arthritis refers to arthritis in multiple joints. Arthritis may have any of various causes, ranging from genetic factors to acquired joint damage or injuries. The type of arthritis involved is largely determined by its cause. After osteoarthritis, which is largely associated with aging and mechanical wear, the most common forms of arthritis are acute septic arthritis and rheumatoid arthritis.
Septic arthritis, also called infectious arthritis, is generally caused by a bacterial infection in the joint, with rare cases being caused by viral or fungal infections. The primary symptom of septic arthritis is joint pain. Around 90% of all cases of septic arthritis involve only one joint. Although septic arthritis may affect any joint, it is most frequently found in the knees (50%) and hips (25%). Taken together, the shoulders, elbows, ankles and wrists account for only around 10% of all cases.
A distinction is made between septic arthritis, arthritis associated with rheumatic diseases (i.e. rheumatoid arthritis), reactive (or post-infectious) arthritis and arthritis associated with metabolic diseases such as gout.
What is arthritis?
All cases of inflammation in the body follow the same pattern: damage in an affected area is accompanied by redness and warmth. These are signs of increased blood flow. Increased numbers of immune cells arrive at the location along with the blood. The occurrence of swelling is a sign of edema, or an excess accumulation of serous fluid in the tissue. This increases the pressure on the nerve endings and leads to pain emanating from the area in question.
The same applies to swelling in the joints. The blood vessels in the synovial membrane lining the joint expand and fill with blood. Blood plasma exits the blood vessels and enters the intercellular spaces of the synovial membrane, causing the membrane to swell. The plasma then moves from the membrane into the joint cavity. This collection of joint fluid or effusion is rich in white blood cells and clotting substances. These are released from the blood at the location of the inflammation. The clotting substances and the white blood cells form a thin crust-like layer covering the synovial membrane, which results in an abnormal growth of the membrane. From an arthroscopic point of view, such excessive growths resemble the intestinal villi (tiny, finger-like projections that come out from the wall of the small intestine). They also have the same function, effectively increasing the overall surface area and leading to increased resorption and secretion of the synovial fluid that gathers in the joint. The white blood cells are deposited in the joint where they attract additional immune cells. The synovial membrane grows over the cartilage and destroys it. Continuing unabated in the manner of a self-perpetuating disease, arthritis will ultimately expose the surface of the bones. With the destruction of the sophisticated structure between them, the bones now impact directly and cause considerable pain.
What causes arthritis?
In the case of rheumatoid arthritis, a chronic autoimmune disease affecting the joints, the synovial membrane reacts to this thin crust-like layer by forming cell aggregates that attack and destroy the cartilage in the joint, as well as the cells of the bone exposed at the edges of the cartilage adjacent to the attachment of the joint capsule. While these cell aggregates ultimately die off, a residue is left that transforms into fiber cells that form a layer (also referred to as pannus tissue) over the destroyed cartilage.
Covering large sections of the cartilage in the joint, the layer of pannus tissue effectively cuts off the supply of nutrients from the synovial membrane to the cartilage and leaves it to starve. The white blood cells attempt to dissolve the dead tissue by releasing aggressive immunoregulatory agents known as cytokines that also degrade the cartilage while at the same time promoting the formation of osteoclasts that break down the bone tissue by resorption. What is left in the end is a joint that has been more or less destroyed. Even the tendons, ligaments and synovial bursa can be affected.
In the case of septic or infectious arthritis, microorganisms (primarily bacteria) enter the joint via the blood or as a result of injuries that open the joint cavity. The most common ways in which bacteria gain direct access to the joints include injury, surgical procedures and injections.
Around 50% of all cases of septic arthritis are caused by the staphylococcus aureus bacterium. The staphylococcus epidermidis bacterium accounts for around 25% of all cases and streptococci account for another 15%. Viruses, including the rubella virus, the mumps virus and the hepatitis B virus, can also cause arthritis.
How will your doctor arrive at a diagnosis?
Effusion in the joint is one very important sign. This can be felt at particular locations on the knees and elbows, and otherwise visualized by ultrasound in other joints. X-rays can also be used to detect characteristic changes in the bones that are connected by the joints. Tests are also carried out to determine the presence of inflammation markers. The key investigation is the aspiration of the joint using a hollow needle (arthrocentesis). This enables your doctor to gather and analyze the synovial fluid that has accumulated in the joint. The diagnostic value of the various parameters - particularly the white blood cell count - allows your doctor to determine whether the joint effusion derives from an inflammatory or non-inflammatory condition. The appearance of the effusion permits further differentiation. A smear may also be taken to determine the exact nature of a given bacterial infection.
What forms of treatment are administered?
Depending on the condition involved, treatment is geared to achieving any of 5 different goals:
- Rapid elimination of inflammatory processes caused by bacterial infections through the use of antibiotics
- Mechanical cleansing (removal of the factors causing inflammation)
- Pressure reduction
- Functional healing
- Removal of excessive synovial membrane growth
Septic arthritis requires immediate surgical intervention: primarily in the form of arthroscopy. Here, the aim is to reduce the high concentration of white blood cells, which secrete damaging cytokines, so as to prevent the destruction of the joint. In this context, the joint is thoroughly rinsed and then drained. If these measures do not suffice, then a decision may be made to perform open or arthroscopic synovectomy. All of the above measures are accompanied by the (usually intravenous) administration of antibiotics for a period of 2-6 weeks. A broad-spectrum antibiotic is usually administered at the start of treatment. This is then replaced by a narrow-spectrum antibiotic as soon as the doctor has identified the exact type of bacterial infection involved.
Quick links to related topics on our website:
Osteoarthritis of the hip, osteoarthritis of the knee, osteoarthritis of the ankle, osteoarthritis of the big toe, osteoarthritis of the facet joints, osteoarthritis of the shoulder
