Septic arthritis is an infection in a joint. Bacteria, or less commonly fungi, can spread from other infected areas in your body to a joint. Sometimes bacteria infect only the joint, leaving other areas of your body unharmed.
In septic arthritis, germs infiltrate your joint — usually just one — and damage it, causing severe pain. Bacteria most commonly target your knee, though other joints can be affected by septic arthritis, including your ankle, hip, wrist, elbow and shoulder. Young children and older adults are most likely to develop septic arthritis.
Signs and symptoms of septic arthritis include:
- Shaking chills
- Severe pain in the affected joint, especially when you move that joint
- Swelling of the affected joint
- Warmth in the area of the affected joint
If you’re taking medications for other types of arthritis, you may not feel severe pain with septic arthritis, because those medications may mask the pain and fever.
The joints of your arms and legs, especially the knees, are most commonly affected by septic arthritis. In rare cases other joints, such as those in your back, neck and head, may be affected.
If you’re at an increased risk of infection and you notice signs and symptoms of infection, such as fever and chills, see your doctor right away. Prompt treatment may prevent the spread of infection and minimize the damage to your affected joint.
Septic arthritis may develop when an infection elsewhere in your body, such as an upper respiratory tract infection or urinary tract infection, spreads through your bloodstream to a joint. Less commonly, a puncture wound, drug injection or surgery near a joint may allow bacteria into the joint.
The lining of your joints (synovium) has little to protect itself from infection. Once bacteria reach the synovium, they enter easily and can begin destroying cartilage. Your body’s reaction to the bacteria — causing inflammation around the joint, increasing pressure in your joint and reducing blood flow to the joint — contributes to the damage of your joint.
A number of strains of bacteria can cause septic arthritis. The most common type involved in septic arthritis is Staphylococcus aureus (staph) — a type of bacteria commonly found on your skin and in your nose.
In the past, septic arthritis was more frequently caused by the bacterium that causes the sexually transmitted disease gonorrhea. But use of safer sex practices has led to a decline in gonorrhea and its complications, including septic arthritis. Still, in younger sexually active people, gonorrhea is a potential cause of septic arthritis. Bacteria are just one cause of joint infections. Viruses also can attack joints (viral arthritis), though this condition usually resolves on its own and causes little joint damage. In rare cases, joint infections can be caused by a fungus (fungal arthritis). Another infectious type of arthritis is reactive arthritis, which causes joint pain in response to an infection in another part of the body, though the joint itself isn’t infected.
Risk factors for septic arthritis include:
- Existing joint problems. Diseases and conditions that affect your joints — including other types of arthritis, gout, pseudogout and lupus — may increase your risk of septic arthritis. An artificial (prosthetic) joint, previous joint surgery and joint injury also increase your risk.
- Taking medications for rheumatoid arthritis. People with rheumatoid arthritis have a further increase in risk because of the medications they take. Rheumatoid arthritis medications may suppress the immune system, making infections more likely to occur. Also, diagnosing septic arthritis in people with rheumatoid arthritis is difficult because many of the signs and symptoms are similar.
- Skin fragility. Diseases and conditions that make skin wounds common give bacteria easy access to your body. Skin conditions such as psoriasis and eczema increase your risk, as do skin infections. People who regularly inject drugs also have a higher risk of infection at the site of injection.
- Weak immune system. A weak immune system may give you a higher risk of septic arthritis because your body can’t defend itself against infections. People with diabetes, kidney and liver problems, and those taking drugs that suppress their immune systems (immunosuppressive drugs) have an increased risk of infections.
The following tests typically help diagnose septic arthritis:
- Joint fluid analysis. To discover exactly what bacterium is causing your infection, your doctor takes a sample of the fluid within your joint (synovial fluid). He or she extracts the synovial fluid through a needle (aspiration) that’s inserted into your joint. Synovial fluid normally appears clear and thick. Bacterial infections can alter the color, consistency, volume and makeup of the synovial fluid. Your doctor examines the synovial fluid and then sends the fluid to a lab for analysis, including tests to determine what organism is causing your infection.
- Blood tests. Your doctor may order blood tests to see if bacteria are present in your bloodstream.
- Imaging tests. X-rays and other imaging tests of the affected joint also may be ordered to assess any damage to the joint.
Prompt treatment with antibiotics usually resolves the infection. If treatment is delayed, however, the infection can quickly lead to joint degeneration — usually within five to seven days — and permanent damage. Complications of septic arthritis often include osteoarthritis and joint deformity. In severe cases, the joint may need to be surgically reconstructed. If the infection affects a prosthetic joint, the prosthetic joint may need to be replaced.
Doctors rely on antibiotic drugs and joint drainage when treating septic arthritis.
Your doctor works to identify the bacterium that’s causing your infection and then selects the most effective antibiotic to target that specific bacterium. Antibiotics may be given through a vein in your arm (intravenously) at first. Later, in some cases, you may be able to switch to oral antibiotics. How long you undergo antibiotic treatment depends on your health, the type of bacterium you’re infected with and the extent of the infection. Typically, treatment lasts about two to six weeks.
Antibiotics carry a risk of side effects, including nausea, vomiting and diarrhea. Allergic reactions also can occur. Talk to your doctor about the side effects to expect from your specific medication.
Removing the infected synovial fluid from your joint serves three purposes: It removes bacteria from your joint, reduces pressure on your joint, and gives your doctor a sample to test for bacteria and other organisms. The most common method of removing joint fluid is through arthroscopic surgery. During this surgery, tiny cameras and special surgical tools are inserted through small incisions around your joint to access and drain the fluid around the joint.
In other cases, doctors may remove fluid from your joint with a needle (arthrocentesis). Arthrocentesis may be repeated, usually daily, until no bacteria are found in the extracted fluid. Hips, which are more difficult to access, may require open surgery to remove the synovial fluid. Open surgery requires larger incisions to pull back the skin and access your joint. Surgery may need to be repeated in certain cases.
Once the infection is under control, your doctor may recommend gentle movement to keep your joint functional. Gentle exercises can keep your joint from becoming stiff and your muscles from becoming weak. Movement also encourages blood flow and circulation, which helps your body’s healing process.
You can help your body fight infection by taking care of yourself during treatment for septic arthritis. Here are some suggestions:
- Follow your doctor’s instruction for exercising your affected joint.
- Eat a healthy diet full of fruits and vegetables.
- With your doctor’s permission, engage in low-impact activities.
- Get enough sleep so that you wake refreshed.
- Reduce stress when possible.
- Use nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen (Advil, Motrin, others) or aspirin, to ease joint pain. Resting the affected joint and applying warm compresses also may help relieve pain and inflammation.