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. To treat septic arthritis and limit joint damage, your doctor will give you antibiotic drugs and drain the infected fluid from your joint.

Signs and symptoms of septic arthritis include:

• Fever
• 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.

When to see a doctor
See your doctor if you have signs and symptoms that may indicate septic arthritis. 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.

Types of bacteria
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.

Other infectious causes of 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.

Having a combination of risk factors usually puts you at a greater risk than having just one risk factor.

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.

If you have painful and inflamed joints, you're likely to start by first seeing your primary care doctor or a general practitioner. However, in some cases you may be referred to an infectious disease or joint specialist. If you see a joint specialist already for an existing illness such as arthritis, you may start by seeing this doctor first.

Because appointments can be brief, and because there's often a lot of ground to cover, it's a good idea to be well prepared for your appointment. Here's some information to help you get ready for your appointment, and what to expect from your doctor.

What you can do

• Write down any symptoms you're experiencing, including any that may seem unrelated to the reason for which you scheduled the appointment.
• Write down key personal information, including other medical conditions you may have and any recent infections.
• Make a list of all medications, as well as any vitamins or supplements, that you're taking.
• Take a family member or friend along, if possible. Sometimes it can be difficult to soak up all the information provided to you during an appointment. Someone who accompanies you may remember something that you missed or forgot.
• Write down questions to ask your doctor.

Your time with your doctor is limited, so preparing a list of questions ahead of time will help you make the most of your time together. List your questions from most important to least important in case time runs out. For septic arthritis, some basic questions to ask your doctor include:

• What is likely causing my symptoms or condition?
• Other than the most likely cause, what are possible causes for my symptoms or condition?
• What kinds of tests do I need?
• How long are my symptoms likely to last?
• What is the best course of action?
• I have these other health conditions. How can I best manage them together?
• What can I do to ease joint pain? What medications can I take?
• Should I see a specialist? What will that cost, and will my insurance cover seeing a specialist? (You may need to ask your insurance provider directly about coverage concerns.)
• Is there a generic alternative to the medicine you're prescribing me?
• Are there any brochures or other printed material that I can take home with me? What Web sites do you recommend visiting?

In addition to the questions that you've prepared to ask your doctor, don't hesitate to ask questions during your appointment at any time that you don't understand something.

What to expect from your doctor
Your doctor is likely to ask you a number of questions. Being ready to answer them may reserve time to go over any points you want to spend more time on. Your doctor may ask:

• When did you first begin experiencing symptoms?
• Have your symptoms been continuous, or occasional?
• How severe are your symptoms?
• What, if anything, seems to improve your symptoms?
• What, if anything, appears to worsen your symptoms?
• Have you had any recent infections?
• Do you have any chronic illnesses?
• Have you ever had joint surgery or joint replacement?

What you can do in the meantime
Avoid activities that seem to make your symptoms worse. To ease joint pain, try resting your affected joint and applying warm compresses. Pain relievers such as ibuprofen (Advil, Motrin, others) and aspirin also may help.

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.

Doctors rely on antibiotic drugs and joint drainage when treating septic arthritis.

Antibiotic drugs
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.

Joint drainage
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.

Recovery
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.

Though these self-care measures can't cure your septic arthritis, they may help you feel better during treatment.