What to Know About Septic Arthritis

Septic arthritis is a rare and severe arthritis that affects one or more of your joints. Bacteria generally cause it, but sometimes, it can develop after exposure to a virus or fungus. The infection will spread to the joints and cause inflammation. Septic arthritis is also called pyogenic arthritis or bacterial arthritis.

It typically affects the large joints of the hips and knees but can affect other joints, such as the shoulder or ankle, as well. Symptoms include severe pain and swelling, limited joint range of motion, fever, and chills. Risk factors include prior joint surgery, a weakened immune system, diabetes, inflammatory arthritis, or an open wound.

Septic arthritis is treated with antibiotics and can be a serious condition if left untreated. It can lead to progressive and irreversible joint damage or become a life-threatening medical emergency.

This article will cover the causes and risk factors for septic arthritis, its effects on joints, symptoms, treatment, and more. 

What Causes Septic Arthritis?

Septic arthritis is caused by bacteria, viruses, and fungi, with Staphylococcus aureus (staph) as the most common infectious cause. Staphylococcus aureus bacteria are linked to pneumonia, skin infections, sepsis, and bone and joint infections. Staph infections can become life-threatening if not adequately treated.

Septic arthritis can develop when an infection, such as a skin infection, spreads into the bloodstream to a joint. This might be because of an open wound related to surgery or injury, which allows germs to enter the joint space.

It typically affects one joint. However, it is possible to experience the condition in multiple joints depending on the bacterium that caused it. For example, Neisseria bacteria can lead to septic arthritis in multiple joints (polyarticular arthritis). With polyarticular septic arthritis, usually both knees are involved, but other joints can also be affected.

Inflammation linked to septic arthritis occurs at the cartilage surface (the connective tissue that allows bones and joints to move over one another smoothly) or the synovium (joint lining). It can also invade the synovial fluid that lubricates the joints.

The most common organisms that lead to pediatric septic arthritis are methicillin-resistant Staphylococcus aureus (MRSA), Streptococcus pneumoniae, group B Streptococcus, Klebsiella pneumoniae, and Gram-negative bacilli.

Common pathogens for adult septic arthritis include Staphylococcus aureus, coagulase-negative Staphylococcus, Streptococcus, and Pseudomonas, and other Gram-negative bacteria.

Who Is at Risk for Septic Arthritis?

Septic arthritis frequently affects children, but adults get it too. Children are at a higher risk for infections that could lead to septic arthritis.

Some risk factors in children and adults increase the risk for infections, including those that lead to septic arthritis.

Risk factors include:

• Arthritis conditions, including osteoarthritis, gout, and autoimmune arthritis like rheumatoid arthritis (RA) and lupus: The medications you take to treat these conditions could also raise the risk for septic arthritis. For example, people with RA are treated with drugs that suppress the immune system and increase their risk for infection, including, disease-modifying antirheumatic drugs (DMARDs) and corticosteroids.
• Previous septic arthritis: If you have had septic arthritis in the past, you are more likely to get it a second time.
• Having a weakened immune system: People with diabetes and kidney or liver problems are at an increased risk for septic arthritis. The medications they take to treat these conditions can add to that risk.
• Having an artificial joint: Bacteria can enter the joint space during joint surgery, or an artificial joint can be infected after an infection from a nearby body area.
• Joint trauma: If you have an open wound or cut near a joint, germs from the skin can enter the joint space through the bloodstream.
• Skin problems: People with fragile skin might be at an increased risk for septic arthritis. This includes people with psoriasis, an autoimmune skin condition that causes overgrowth of skin cells. 
• Injection drug use: This is a newer known risk factor often linked to non-medically administered injections that are not sterile and can introduce bacteria through the skin into the bloodstream. These bacteria might be more antibiotic-resistant or infectious, leading to disease complications and life-threatening medical situations. 
  

Two or more of the above risk factors put you at a greater risk for developing septic arthritis compared to one risk factor alone. 

What Joints Are More Likely to Have Septic Arthritis?

In general, infections in native joints (joints you're born with as opposed to prosthetic, or artificial, joints that are implanted) commonly occur in the knees, hips, shoulders, ankles, elbows, and wrists. However, the location may depend on the type of pathogen, underlying conditions, or exposure type. Additionally, children may experience septic arthritis in different joints than adults. 

Research shows that children are more likely to get septic arthritis in the hip or knee. Children can also experience elbow septic arthritis caused by a staph infection.

Pathogens that cause septic arthritis in adults are typically linked to medical history, health status, orthopedic surgery, and injection drug misuse. Adults are more likely to get septic arthritis in the knee or the small joints of the interphalangeal joints (hinge joints) of the fingers. 

Septic arthritis causes excess fluid in and around the knee joint. "Knee joint effusion" is the medical term for this condition, and it is seen on ultrasound in 91% of people with septic arthritis.

One 2021 Orthopedics report finds the joints most affected by septic arthritis caused by injection drug use include the knees, ankles, shoulders, elbows, wrists, and fingers.

Additional research suggests septic arthritis linked to injection drugs may also affect the sacroiliac joints connecting the pelvis and lower spine, the facet joints in the lower spine, and the sternoclavicular joint connecting the collarbone to the breastbone.

What Are the Symptoms of Septic Arthritis?

The symptoms of septic arthritis will occur in the infected joints. You may also experience systemic (whole-body) symptoms. 

Symptoms of septic arthritis include:

• Severe pain and tenderness in the affected joint, especially with movement 
• Visible swelling from increased fluid in the joint
• Warmth (the joint is warm to the touch)
• Stiffness of the affected joint that makes movement difficult
• Fatigue and generalized weakness
• Fever and chills
  

If septic arthritis affects a prosthetic joint, you may experience minor pain and swelling that worsens over time. In this case, the infection occurs long after the surgical area has healed.

The prosthetic joint may loosen, causing additional pain with movement or putting weight on the joint. In severe cases, the joint will become dislocated. 

With a postoperative (following surgery) prosthetic joint infection, the affected joint will show signs of infection at the skin above the affected joint, such as swelling, redness, pain, and discharge. There will also be delayed healing of the surgical area. 

How Is Septic Arthritis Diagnosed?

An arthrocentesis procedure can help a healthcare provider confirm a diagnosis of septic arthritis. It is administered by inserting a needle into the affected joint to withdraw a sample of synovial fluid.

The sample is taken to a lab to look for white blood cells, which will be elevated with septic arthritis. The lab will also look for bacteria and other organisms to determine the cause of septic arthritis.

X-rays and other imaging might be requested to look for joint damage. X-rays can show damage that has already occurred, while magnetic resonance imaging (MRI) scans can show joint damage at its earliest stages. 

Ultrasound might be used to look for joint effusion and synovial swelling in children. It is more sensitive to detecting septic arthritis in children than X-rays and MRIs. Unfortunately, it cannot rule out osteomyelitis (bone infection and inflammation) or nearby intramuscular abscesses (localized fluid and pus collections in the muscles).

Blood work will be requested to look for and monitor inflammation in the body. This includes C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR or sed rate) testing.

If your healthcare provider suspects a prosthetic joint infection, they may request a nuclear scan. This test involves swallowing or injecting a small amount of radioactive fluid for a specialized scan.

What's the Treatment for Septic Arthritis?

Treatment for septic arthritis includes a combination of strong antibiotics and draining the fluid in the affected joint. Intravenous (IV) antibiotics are administered right away to slow down the spread of the infection. This means you will be admitted to the hospital for treatment.

If your healthcare provider has not determined the pathogen causing the infection, you will be given an empiric antibiotic—a broad-spectrum antibiotic that treats various infections.

Once you have finished your IV antibiotic treatment and go home, your healthcare provider will prescribe oral antibiotics. Antibiotic courses of three to four weeks are usually enough to treat septic arthritis, but treatment may continue for up to six weeks in more severe cases.

Drainage of the fluid in the affected joint can quickly rid the joint of infection. An arthrocentesis procedure can usually accomplish this, but in some cases, a surgical procedure might be needed to rid the affected joint of the infection.

Additional treatment to facilitate recovery and manage pain might include:

• Nonsteroidal anti-inflammatory drugs (NSAIDs) to reduce inflammation and pain
• Resting the affected joint 
• Splinting the affected joint to reduce painful movement and improve healing time
• Physical therapy to manage pain and regain mobility in the affected joint

Surgery and Draining the Infected Fluid

Surgery is typically done in cases in which the septic arthritis is causing severe pain, reduced joint mobility, and inability to bear weight on the affected joint.

Arthroscopic surgery can treat an infection in the joint cavity. A surgeon will drain fluid (if the fluid buildup is significant) and remove infected tissue. They will make small incisions near the affected joint and use a small tube with a camera to guide them.

An open surgical procedure might be undertaken if there is joint damage. This surgery will remove any damaged joint sections or replace the joint once the infection has been treated.

If a prosthetic joint is infected, treatment includes removing and replacing it with a new implant. If the prosthetic joint does not need to be removed, it is cleaned out and any damaged tissue is removed. The prosthetic joint is left in place.

What Happens If Treatment Is Delayed?

Untreated septic arthritis can lead to severe complications or become life-threatening. It can cause permanent damage to bone and joint tissues. The damage could alter the mobility of a weight-bearing joint (hip or knee). Septic arthritis may also appear with osteomyelitis.  

Although rare, untreated septic arthritis can lead to septic shock, an extremely dangerous reaction to an infection. This depends on the type of bacteria or the person's health status. For example, a person with a weakened immune system may experience severe sepsis that could quickly lead to death. Fortunately, this complication can be prevented by getting prompt medical care. 

Can I Prevent Septic Arthritis?

It might be possible to prevent septic arthritis. This starts by avoiding or treating cuts, wounds, or other damage to the skin. If you or your children experience a cut or a burn, the skin area should be washed quickly and thoroughly. Medical attention should be sought for cuts or burns that are deep or especially severe. 

If you have an autoimmune disease or diabetes, you want to keep your condition well-managed to decrease infection risk. Reach out to your healthcare provider at the first signs of an infection, especially fever and severe joint pain.

When to See a Healthcare Provider

Septic arthritis can become a medical emergency if left untreated. You should reach out to your healthcare provider or head to your local emergency department if you experience symptoms of the condition.

Intense pain and swelling, accompanied by fever and chills, can come on suddenly and worsen quickly. This is especially important if these symptoms affect a prosthetic joint or if you are someone with a weakened immune system. 

Summary

Septic arthritis is an infectious arthritis that affects one or more joints. Bacteria often cause it, but it might also occur because of a virus or fungus. It develops when an infection spreads to the joints and causes severe inflammation. The infection can invade cartilage tissue, synovial joint linings, and synovial fluid.

This type of arthritis typically involves a knee or hip joint, but any joint can be affected. It can sometimes affect multiple joints or a prosthetic joint one year or more after joint replacement surgery. 

Symptoms include pain, swelling, limited joint range of motion, fever, and chills. Septic arthritis is more common in children and people with prior joint surgery, an open wound, diabetes, or an autoimmune disease.

Septic arthritis is treated with antibiotics and the removal of excess joint fluid, but some people may need surgery to clean out the affected joint or remove damaged tissue. Treatment is crucial because septic arthritis can lead to irreversible joint damage or life-threatening sepsis.

If you or a child develop sudden joint pain with fever and chills, you should contact your healthcare provider immediately or head to a nearby emergency room.