Knee replacements have emerged as a mainstream surgery. According to the Agency of Research and Quality (AHRQ), over 600,000 procedures were performed in 2009. That number is expected to grow into the millions by the year 2030. According to the American Academy of Orthopedic Surgeons (AAOS), serious complications occur in less than 2 percent of cases. However, it’s still important to be aware of the risks before you enter the operating room.

The 30-day mortality rate for a total knee replacement (TKR) is about 1 in 400, or 0.25 percent. That means that 99.75 percent of those who undergo this surgery survive the treatment. Researchers in the U.K. reported in The Bone & Joint Journal that they looked at almost 2,500 people who had a TKR over a 10-year span. They found that 99 percent survived at least one year. Ninety percent were alive after five years. Eighty-four percent were still living after 10 years. Overall, mortality rates are highest in the 30 to 90 days following surgery.

Relatively few complications happen during the hospital stay after a TKR. Healthline analyzed data on over 1.5 million Medicare and privately insured people to take a closer look at these complications. Based on this analysis, 4.5 percent of those who’ve had a TKR and are under the age of 65 experience complications during this period. However, the same data set showed that the complication rate more than doubles for older adults.

About 1 percent of people get a postoperative infection. The same-day death rate for this same group is extremely rare (0.001 percent). Blood clots are a risk, as they are with most orthopedic surgeries, but common preventative measures have reduced their risk. Less than 2 percent of people get them now. Cases of osteolysis — when plastic or metal fragments are released from the knee implant into the body and cause inflammation — are also uncommon.

However, this procedure does come with possible complications.

Complications from anesthesia

A surgeon may use general or regional anesthesia to put you into a deep sleep or numb your leg. This is so you won’t feel any pain during surgery. Modern anesthesia is generally safe, but it can cause side effects and negative reactions. It can be fatal in some rare cases. The most common side effects include:

  • vomiting
  • dizziness
  • shivering
  • sore throat
  • aches and pains
  • discomfort
  • drowsiness

Adverse effects, or negative reactions, include:

  • dental trauma
  • croup (swelling of the windpipe)
  • allergic reactions to latex
  • wheezing
  • vocal cord injury
  • stomach problems
  • injuries to arteries, veins, or nerves

The general anesthesia may also cause an irregular heartbeat in some people.

You should review your medical history before surgery to make sure that any prescriptions or over-the-counter medications you take don’t interfere with the surgery. Tell your anesthesiologist if you smoke, use recreational drugs, or heavily consume alcohol. These can put you at greater risk for problems related to anesthesia.

Blood clots

The medical term for blood clots when they occur in the legs is deep vein thrombosis (DVT). Clots in the lungs are called pulmonary embolism (PE). Surgery or an injury of any kind increases the risk of a blood clot. That’s because the clotting process is stimulated as your body attempts to stop the bleeding and close the surgical wound. A clot is normally formed by blood cells and clotting factors working together to create a protective scab over a healing wound. The surgical procedure may stimulate clots to form in error in blood vessels, which then may block the normal flow of blood.

Orthopedic surgeries like knee replacements are particularly likely to cause blood clots. Blood clots typically occur within two weeks of surgery, but they can also take place within a few hours or even in the operating room. Clots caused by DVT could delay your release from the hospital by a few days.

According to Healthline’s analysis of Medicare and private pay claims data, less than 3 percent of people reported DVT during their hospital stay. Less than 4 percent reported DVT within 90 days of surgery.

Clots contained in the legs are a relatively minor risk. However, a clot that dislodges and travels through the body to the heart or lungs can cause serious health concerns. It can be fatal in rare cases. There are a few preventative measures that you and your doctor can discuss:

  • Blood thinning medications. Your doctor will likely recommend that you take medications like warfarin (Coumadin), heparin, enoxaparin (Lovenox), fondaparinux (Arixtra), or aspirin to reduce the risk of clots after surgery. Talk with your doctor to understand any side effects caused by these medications.
  • Techniques to improve circulation. Your doctor may suggest treatments like support stockings, lower leg exercises, calf pumps, or elevating your legs to help increase circulation and prevent clots from forming.

Be sure you discuss your risk factors for clots before your surgery. Some conditions, such as smoking or obesity, increase your risk.

Finally, talk to your surgeon about the signs and symptoms of a blood clot so you can monitor yourself after you leave the hospital. The AHRQ provides additional information on the prevention, symptoms, and treatment of blood clots.


The number of people who get an infection after a knee replacement is very low (rates for computer-assisted surgery are even lower). According to Healthline’s analysis of Medicare and private pay claims data, 1.8 percent of patients are reported to develop an infection within 90 days of surgery.

Because the knee joint is exposed during the procedure, the surgical team takes serious measures to prevent infections:

  • Hospitals typically use special air filters for surgical rooms that limit particles in the air.
  • Surgeons and their assistants follow a strict procedure of “scrubbing in” and dressing in protective wear in order to meet sterility standards of the operating room.
  • The surgical instruments and the implants themselves are all sterilized before they enter the operating room.
  • Your doctor will also likely prescribe antibiotics before, during, and after the operation to help prevent infection.

People with rheumatoid arthritis or diabetes have a greater risk of infection in the weeks following a procedure. Researchers believe they have higher complication and mortality rates because of their altered immune system.

Also keep in mind that if you have an infection in another part of the body at the time of your knee operation — in your mouth, kidneys, or prostate, for example — it could lead to an infection in your knee months or even years later. Talk with your doctor if you’ve recently had or plan to have any other medical procedures within a few months of your TKR.

Complications from a transfusion

On occasion, a blood transfusion is necessary following the TKR procedure. If you receive a blood transfusion, there’s a tiny risk that you will become sick due to an incompatible blood match during a transfusion.

Blood banks routinely screen for all potential infections and illnesses, including AIDS and hepatitis B and C. In extremely rare cases, however, these conditions go undetected.

It’s possible to have an allergic reaction or a reaction called a hemolytic transfusion reaction to the donor blood, although this is also rare.

Signs and symptoms of an adverse transfusion reaction usually occur within 24 hours. Symptoms of these reactions include:

  • hives
  • fever
  • chills
  • shortness of breath
  • red urine

Some hospitals ask you to bank your own blood before surgery. Ask whether it’s advisable to bank your own blood in advance if your surgeon thinks you might need blood during surgery.

Allergy to metal components

Some people may suffer a reaction to the metal used in the artificial knee joint. The metal materials used in implants are typically made from titanium or cobalt-chromium-based alloy. You probably already know if you have a metal allergy. If so, make sure to tell your surgeon about the allergy well before your surgery. Take the time to discuss the topic with your surgeon or medical team if you are unsure.

Wound and bleeding complications

The sutures or staples used to close the wound are typically removed after about two weeks. There are some potential complications, however:

  • Wounds may sometimes be slow to heal and bleeding complications can occur for several days following surgery. The hospital staff will monitor your wound during the time you are there. Blood thinners can contribute to problems. The surgeon might need to reopen the wound and drain fluid.
  • You could also experience a Baker’s cyst, which is a buildup of fluid behind the knee. This may require draining with a needle to remove the fluid.
  • If the skin does not heal properly, you might need a skin graft.

Artery injuries

Because the major arteries of the leg are directly behind the knee, there’s a slight risk that these vessels could be damaged. A vascular surgeon can usually repair the arteries if there is damage.

Nerve or neurovascular damage

It’s also uncommon for the nerves to be damaged. However, it’s possible for the nerve or blood vessel that’s associated with the muscles leading to the foot to feel numb afterward. The problem usually disappears after a few months as nerves and tissue heal.

Knee stiffness and loss of motion in the knee

Scar tissue or other complications can sometimes affect motion in the knee. This problem can often be resolved with special exercises or physical therapy. Severe cases of stiffness, called arthrofibrosis, may require a follow-up procedure so the scar tissue can be broken up or the prosthesis inside the knee can be adjusted.

Prosthesis problems and implant failure

Another risk with any joint replacement surgery is improper placement or a malfunction of the implant. For example, the artificial kneecap may not track correctly after surgery — in other words, your new knee might not bend properly.

Another possible implant problem is that the prosthesis might loosen from the bone over the long term. It will require an adjustment if that happens.

Other parts in the artificial knee can also wear or break, including the polyethylene components.

These failures are extremely rare. According to Healthline’s analysis of Medicare and private pay claims data, only 0.7 percent of patients experience mechanical complications during their hospital stay. Most failures occur within weeks of surgery. A follow-up surgery is usually required to fix the problem when this does happen. This surgery is called a revision surgery.

A revision can also be required for reasons other than mechanical failure, including (among others):

  • infection
  • continued pain
  • knee stiffness
  • wear
  • instability
  • loosening of the implant or mechanical components

Analysis of data from Medicare shows that the average rate of revision surgery within 90 days is 0.2 percent. However, the rate increases to approximately 3.7 percent within 18 months.

There can also be long-term wear and loosening of the implant over several years. According to a meta-analysis of worldwide joint registry databases published in the The Bone & Joint Journal in 2011, the long-term revision rate is 6 percent after five years and 12 percent after 10 years.

You can reduce future problems by maintaining your weight. You should also avoid activities that can put too much stress on the joint, such as running, jumping, court sports, and high-impact aerobics.

It’s important to know the benefits and the risks before undergoing surgery despite the high degree of safety and success associated with TKRs. Only then can you make the right decision.