A knee infection is a serious medical condition that often requires immediate and aggressive treatment. When bacteria contaminate the synovial fluid that lubricates your knee joint, an infection called a septic joint can be the result.

Knee infections sometimes happen as a complication of surgery, inflammation, or for other reasons.

Treatment for a knee infection varies widely depending on the underlying cause. Keep reading to find out about the symptoms, causes, and treatments for knee infections.

A knee infection is a serious health condition and should be treated by a doctor quickly to avoid serious complications.

The main symptom of a knee infection is severe pain whenever you try to move your knee joint. Other symptoms may include:

  • inability to move your knee due to pain or stiffness
  • chills and nausea
  • fever that lasts for more than 24 hours
  • swelling around your knee
  • redness or irritation at your knee

Knee infections can come about from injuries, surgeries, Staphylococcus infections, and infections elsewhere in your body. Here are some of the most common conditions related to knee infections.

Soft tissue infection

Soft tissue infections, also called cellulitis, are most often caused by staph bacteria. These bacteria live on your skin, even when your skin is healthy, but can enter your knee joint area through any open wound on your knee.

Soft tissue infections send more than 14 million people to the doctor for treatment each year in the Untied States. Diabetes medications and immune-suppressing prescription drugs can put you at a higher risk for this kind of infection.

Knee infection after surgery

Knee replacement surgery is a common surgery that doesn’t present complications for most people. In less than 1 percent of joint replacement surgeries, an infection occurs around the area of the artificial implant. However, as joint replacements are on the rise, so is the rate of infection.

Since artificial joints are made of metal and plastic, they don’t have any sort of immune capability to fight off harmful bacteria. Artificial joints can become infected at the time of your surgery, or even years after your surgery.

Surgeries performed to repair torn cartilage or tendons can also introduce bacteria to the knee joint. ACL repair and meniscus repair are among the common knee surgeries that can result in an infection.

Bacterial joint inflammation

Bacterial joint inflammation is also called septic arthritis. Trauma to your knee joint due to an animal bite, puncture wound, or an existing infection on your skin can cause this kind of knee infection. Existing joint conditions, such as rheumatoid arthritis, and immune-suppressing medications can increase your risk for developing an infection.

Knee bursitis

Knee bursitis is any kind of inflammation that affects the bursae in your knee. Bursae are fluid-filled sacs that pad and protect your knee.

Bacteria can penetrate these sacs and create an infection. Warmth and swelling then occur as the infection spreads throughout the rest of your knee joints.


Sometimes infections that start in the bursae or other parts of your knee can reach the bones. Traumatic injuries that expose your bone to the air can also result in an infection. These bone infections are called osteomyelitis. They’re rare, but very serious.

Knee infections are diagnosed by testing the fluid in your knee. Aspiration of the fluid is performed by inserting a needle into the affected joint space. The fluid that’s removed is tested for white blood cells, viruses, fungi, and bacteria.

A simple blood test may also be done to determine if you have any kind of infection.

Sometimes an X-ray can be used as a tool to assess joint damage caused by a diagnosed infection.

Infections in your joints need to be addressed by a doctor. Trying to treat a knee infection at home could result in your infection spreading into your bloodstream, causing severe complications.


Once you have a diagnosis, your doctor may prescribe antibiotics to bring down the bacteria count in your knee and keep the infection at bay.

You can take antibiotics intravenously until your infection begins to improve. Oral antibiotics may be continued for up to six weeks until you’re cleared from the infection completely.

Joint drainage

If your knee is infected, you’ll need to have the infected fluid surrounding your joint removed. A scope procedure called an arthroscopy may be used to suction and drain the infected fluid out of your body.

In some cases, the fluid can be removed using a large needle. In more serious cases where the infection has progressed, you may need an open surgery to remove infected fluid as well as damaged tissue.

If you have any of the symptoms of a knee injury, contact your doctor right away. Get emergency medical help if you have:

  • chills
  • nausea
  • high fever
  • stiffness that keeps you from moving your joint

If you’ve recently had a joint replacement or knee surgery, call your surgeon’s office or the hospital where the surgery was performed as soon as you notice pain, swelling, or redness. Describe your symptoms and follow any instructions from the doctor.

A knee infection is a serious health condition. Once a joint has become septic, antibiotic treatment and occasionally surgery are the only way to manage symptoms and keep the condition from escalating. If you wait to seek treatment, your knee joint may be permanently damaged, and you could go into septic shock.

It’s important that you get a prompt diagnose and start treatment. With quick medical attention, you can make a complete recovery from an infection in your knee.