Infections after knee replacement surgery are rare. They occur in about 1 out of every 100 people who have a knee or hip replacement.

That said, anyone who is thinking about having surgery to replace a knee should learn about the signs of possible infections and respond quickly if they arise.

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, an infection can develop in the skin around 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. In many cases, a surgeon may need 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. This is when 60 to 70 percent of prosthetic joint infections occur. That said, infections can develop at any time after surgery.

Infections occur around an artificial knee because bacteria can attach to it. An artificial knee doesn’t respond to your immune system like your own knee would. If bacteria gets around your artificial knee, it may multiply and cause an infection.

An infection anywhere in your body can travel to your knee. For instance, bacteria can enter the body through a cut in the skin — even a very small one — and cause an infection. Bacteria can also get into your body during major dental surgery, such as a tooth removal or a root canal.

Your chance of a major infection after knee replacement is higher if you have certain health problems. Tell 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

For 3 to 6 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.

Tell your doctor if you have signs of an infection.

The signs and symptoms of a superficial infection include:

  • 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

It’s normal to have some pain after knee surgery, but if it gets worse over time, this may be a sign of 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 the surgical incision. They may give you some tests to locate the infection or to learn the type of bacteria causing it.

These tests may include:

The best treatment for an infection after total knee replacement depends on the type of infection and its severity. Treatment is more complicated if the infection has been present for a long time.

Antibiotics

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.

Surgery

Major infections usually require surgery. The most common treatment for deep infection after knee replacement surgery in the United States involves two surgeries.

In the first surgery, your doctor:

  • removes the implant and cleans the infected area
  • puts a spacer, which is a cement block that’s been treated with antibiotics, 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 will also need to receive antibiotics by IV for 4 to 6 weeks.

In the second surgery, called revision knee surgery, the doctor will remove the spacer and place a new knee implant.

Debridement

They may not need to remove the knee if the deep infection develops shortly after surgery. Instead, a surgical washout, called debridement, may be enough.

In this procedure, the surgeon removes infected tissue and cleans out the implant, and then provides IV antibiotics for 2 to 6 weeks. Typically, the plastic or polyethylene component is exchanged.

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 into your system.

Steps to take before surgery

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

Before your knee surgery, the following steps can help prevent infections:

  • Antibiotics. Your healthcare team will usually give you antibiotics in the hour before surgery, and then at 24 hour intervals afterwards.
  • Testing for and reducing nasal bacteria. There is some evidence that testing for Staphylococcus bacteria in the nasal passages, and using intranasal antibacterial ointment before surgery, could reduce infections.
  • Washing with chlorohexidine. Some evidence says that washing with cloths soaked in chlorhexidine in the days leading up to surgery could help prevent infection. Brands include Betasept and Hibiclens.
  • Avoid shaving. Opt not to shave your legs before surgery as this can increase the bacterial load.

The surgeon may recommend rescheduling your surgery if there are any changes in your medical condition, cuts or scratches on the skin, signs of a urinary tract infection, or symptoms of a cold.

Steps to take after surgery

After surgery, the following steps can help reduce the chances of infection:

  • Follow your surgeon’s guidance on how to take care of your incision.
  • Treat any cuts, wounds, burns, or scrapes as soon as they happen. Clean with an antiseptic product and then cover it with a clean bandage.
  • Keep up with preventive dental health and don’t delay in 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.

See your doctor if you think you might be developing any kind of infection after total knee replacement, including urinary tract infections, ingrown toenails, and skin infections.