Infections after knee replacement surgery are rare. They occur in about 1 out of every 100 people who have the surgery. But anyone who is even thinking about having surgery to replace a knee should learn about infections.

An infection after knee replacement surgery can be a serious complication. Treating an infection can include multiple surgeries that can keep you out of action for a while. Here’s what you need to know to help protect your new knee so you can enjoy its mobility for years to come.

Superficial infection

After knee replacement surgery, it’s possible to develop an infection in the incision. Doctors call these superficial, minor, or early-onset infections. Superficial infections usually occur soon after your surgery. You may develop a minor infection in the hospital or when you go home. The treatment is simple, but a minor infection can lead to a major one if it’s not treated.

Deep knee infection

You can also develop an infection around your artificial knee, also called a prosthesis or implant. Doctors call these deep, major, delayed-onset, or late-onset infections. Deep infections are serious and can occur weeks or even years after your knee replacement surgery. The treatment may involve several steps. You may need surgery to remove the infected artificial knee.

Everyone who has a knee replaced is at risk for a deep infection. Most infections occur in the first two years after surgery. Still, you’re at risk for an infection as long as you have the joint.

The implant itself puts you at risk for infection because bacteria can attach to it. An artificial knee doesn’t respond to your immune system like your own knee would. So if bacteria gets around your artificial knee, it may multiply and cause an infection.

Plus, an infection anywhere in your body can travel to your knee. A common way bacteria gets into your body is through a break or wound in your skin, even a very small one. Bacteria also often gets in your body during major dental surgery. For example, your risk of infection increases when you have a tooth pulled or a root canal.

Your chance of a major infection after knee replacement is higher if you have certain health problems. Make sure you tell and remind your surgeon if you have any of these conditions:

Your risk is also higher if you:

  • smoke
  • have already had a minor or major infection in your prosthesis
  • have previously had knee surgery
  • are getting treatments that suppress your immune system, such as immunosuppressant medications like corticosteroids or treatments such as chemotherapy

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For three to six months after knee replacement surgery, it’s normal to have mild swelling in your knee or ankle and some redness and warmth around the incision. It’s also normal for the incision to itch. If you can’t walk without pain in the time frame you and your doctor talked about, make sure to follow up and tell them.

Also tell your doctor if you have signs of a superficial infection, such as:

  • increased redness, warmth, tenderness, swelling, or pain around the knee
  • a fever higher than 100˚F (37.8˚C)
  • chills
  • drainage from the incision after the first few days, which may be grayish and have a bad smell

Deep infections may not have the same symptoms as superficial ones. You should also watch out for:

  • a recurrence of pain after your pain had stopped
  • pain that gets worse over a month

Worsening pain is not normal. Most people who have a knee infection have pain, but most people with pain don’t have an infection. Always talk to your doctor about knee pain.

Your doctor may be able to tell you have an infection if they see redness and drainage around your incision. You may need tests to locate the infection or to learn the type of bacteria causing it. These tests may include:

Your doctor can usually treat superficial infections with antibiotics. You may be able to take them by mouth, or you may need antibiotics through an intravenous (IV) line.

If you have a major infection, you’ll most likely need surgery. Treatment is more complicated if you’ve had the infection for a long time.

The most common treatment for deep infection after knee replacement surgery in the United States involves two surgeries, or two stages. In the first surgery, your doctor:

  • removes the implant
  • cleans the infected area
  • puts a cement block that’s been treated with antibiotics, known as a spacer, where the implant was to help kill bacteria in your joint and nearby areas

You usually won’t be able to bear weight on the leg while the spacer is in place. You may be able to get around using a walker or crutches. You’ll also need to receive antibiotics by IV for about six weeks.

The second surgery, called revision knee surgery, is to remove the spacer and place a new knee implant.

If you develop a deep infection just weeks after your knee replacement and your doctor finds it early, you may not have to have the implant removed. Instead, your doctor may recommend a surgical washout, called debridement. This procedure removes infected tissue and cleans out the implant. After debridement, you’ll need IV antibiotics for about six weeks.

Your doctor will take steps during your knee replacement surgery to reduce the chances of infection. You can do things before and after the surgery to make it harder for bacteria to get in your system.

In the weeks before surgery, see your dentist to check for cavities or other problems that need attention. Remember, infection from your mouth, or anywhere in your body, can go to your knee.

A few days before surgery, take these infection precautions:

  • For five days before your surgery, shower with chlorhexidine (Betasept, Hibiclens), an antibacterial and antiseptic cleanser. You can get this without a prescription. Don’t use this after surgery.
  • A few days before surgery, gargle two times a day with an antiseptic mouthwash.
  • Don’t shave your legs before surgery. Those tiny irritations can dramatically increase your risk of infection.
  • If you have any cuts or abrasions on your knee, cancel your surgery until they heal.

After surgery, you can take these steps to reduce your chance of infection:

  • Follow your surgeon’s guidance on how to take care of your incision.
  • Promptly treat any cuts, wounds, burns, or scrapes as soon as they happen. Clean with an antiseptic, then bandage. See your doctor if you think you might be developing any kind of infection, even for an ingrown toenail.
  • Keep up with preventive dental health. If you have a problem, don’t delay seeing your dentist. Your dentist or orthopedic surgeon may want you to take antibiotics about an hour before any dental procedures to reduce your chance of infection.