Risks and Complications

Knee replacements have emerged as a mainstream surgery. According to the Knee Replacement StatisticsAgency of Research and Quality (AHRQ), over 600,000 procedures were performed in 2009 and the 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 two percent of cases. Yet, it’s important to be aware of the risks before you enter the operating room.

The 30-day mortality rate for total knee replacement is about one in 400, or .25 percent. That means that 99.96 percent of patients survive the treatment. Researchers in the UK recently reported in The Journal of Bone & Joint Surgery that among 2,428 total knee replacement patients over a 10-year span, 99 percent survived at least one year; 90 percent were alive after 5 years; and 84 percent were still living after 10 years. Overall, mortality rates are highest 30 to 90 days following surgery.

In addition, relatively few complications are known to occur during the hospital stay. Based on Healthline’s analysis of over 1.5 million Medicare and privately insured patients, 4.5 percent of patients under the age of 65 experience during this period. However, the same data set showed that the complication rate more than doubles for elderly patients. 

Post-operative infection takes place in about one percent of patients. The same-day-death rate for this same group is extremely rare (.001 percent). Although blood clots represent a significant risk—as with most orthopedic surgeries—common preventative measures have reduced the occurrence to less than two percent of patients. Cases of osteolysis—when plastic or metal fragments are released from the knee implant into the body and cause inflammation—are also uncommon. 

Potential problems include:

Complications From Anesthesia

A surgeon may use general or regional anesthesia to put you into a deep sleep or numb your leg. This ensures that you won’t feel any pain during surgery. Although modern anesthesia is generally safe, it can cause side effects, negative reactions, and, in rare cases, even death. 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 and injuries to arteries
  • veins
  • nerves

Some patients also experience an irregular heartbeat from general anesthesia.

It’s important to review your medical history prior to surgery to make sure that any prescriptions or over-the-counter medications you take do not interfere with the surgery. Those who smoke, use recreational drugs, or heavily consume alcohol should inform their anesthesiologist, because they are at greater risk for problems related to anesthesia.

Blood Clots

The medical terms for blood clots are deep vein thrombosis (DVT) when they occur in the legs and pulmonary embolism (PE) when they occur in the lungs. Surgery or an injury of any kind increases the risk of a blood clot. That’s because, as your body attempts to stop the bleeding and close the surgical wound, the clotting process is stimulated, releasing an increased number of fibrin strands into the blood stream. Normally, the clot formed by the blood cells and fibrin strands creates a protective scab over a healing wound. But if there is too much clotting material, it may cause blood to clump together in your blood stream.

Orthopedic surgeries, such as a knee replacement, are especially likely to cause blood clots. Typically, blood clots occur within two weeks of surgery but they can 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 patients are reported to experience DVT during their hospital stay. Less than 4 percent report DVT within ninety days of surgery.

Clots contained within the legs represent a relatively minor risk. However, a clot that dislodges and travels through the body to the heart or lungs can cause serious health concerns and, in rare instances, death. 

To reduce the risk of clots after surgery, your doctor will likely recommend that you take blood-thinning medications such as warfarin (Coumadin), heparin, or enoxaparin (Lovenox). Consult with your doctor to understand any side effects caused by these medications. Common preventative measures your doctor may recommend include support stockings, lower leg exercises,calf pumps, or elevating your legs. All of these techniques help to increase circulation and prevent the formation of clots. Prior to your surgery, be sure you discuss your risk factors for clots, so that your surgeon can take proper preventive measures. Some conditions, such as smoking or obesity, increase your risk.

Lastly, talk to your surgeon about the signs and symptoms of a blood clot, so that you can monitor yourself after you leave the hospital. The Agency for Healthcare Research and Quality (AHRQ) provides additional information on the prevention, symptoms, and treatment of blood clots.


The number of knee replacement patients who experience an infection 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 ninety days of surgery. Because the knee joints 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, and 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. Likewise, all instruments used in surgery (as well as the implants themselves) are sterilized prior to entering the operating room. In addition, doctors will likely prescribe antibiotics before, during, and after the operation in order to help your body prevent against infection.

Patients with rheumatoid arthritis or diabetes have a greater risk of infection in the weeks following a procedure. Researchers believe that higher complication and mortality rates for these patients are associated with a weakened 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 the mouth, kidneys, or prostate, for example—it could lead to an infection in the knee, even months or years later. Talk with your doctor if you have recently had or plan to have any other medical procedures within a few months of your TKR. 

Complications from a Transfusion

Not everyone needs a blood transfusion during a TKR. But, if you do, there’s a tiny risk—about one in 14,000—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, but in extremely rare cases these conditions go undetected. It is possible to have an allergic reaction, or also what is a called a hemolytic transfusion reaction, to the donor blood, although this too is rare. Signs and symptoms of an adverse transfusion reaction usually occur within 24 hours and include hives, fever, chills, shortness of breath, and red urine.

Many hospitals ask patients to bank their own blood before surgery. If your surgeon thinks that you might need blood during surgery, ask whether it’s advisable to bank your own blood in advance.

Allergy to Metal Components

Occasionally, a patient suffers 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. Most likely, you will know if you have a metal allergy. If that is the case, make sure to tell your surgeon about the allergy well before your surgery. If you are unsure, take the time to discuss the topic with your surgeon or medical team.

Wound and Bleeding Complications

Typically, the sutures or staples used to close the wound are removed after about two weeks. In some cases, however, wounds may 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 and, in some cases, the surgeon might need to re-open 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. In addition, if the skin does not heal properly, you might require a skin graft at the wound site.

Artery Injuries

Because the major arteries of the leg are positioned directly behind the knee, there’s a slight risk that damage could occur to these vessels. If damage does take place, a vascular surgeon can usually repair the arteries.

Nerve or Neurovascular Damage

Damage to the nerves is also uncommon. However, it is possible for the nerve or blood vessel that’s associated with the muscles leading to the foot to experience numbness following a procedure. The problem usually disappears after a few months as nerves and tissue heals. 

Knee Stiffness and Loss of Motion in the Knee

In some cases, scar tissue or other complications diminish motion within the knee. This problem can often be resolved with special exercises and/or physical therapy. Severe cases of stiffness, also called arthrofibrosis, may require a follow-up procedure in order to break-up scar tissue or adjust the prosthesis inside the knee.

Prosthesis Problems/Implant Failure

An inherent risk with any joint replacement surgery is improper placement or a malfunction of the implant. For example, the artificial kneecap may not track correctly following surgery—in other words, your new knee might not bend properly. Another possible implant problem is that, over the long-term, the prosthesis might loosen from the bone and require an adjustment. In addition, other parts within the artificial knee can 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. When this occurs, a follow-up surgery is usually required to address the problem. 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

Analysis of data from Medicare shows that the average rate of revision surgery within 90 days is.2 percent.  However within 18 months, the rate increases to approximately 3.7 percent.

Long term wear and loosening of the implant can occur over the period of several years. According to a meta-analysis of worldwide joint registry databases, published in the Journal of Bone & Joint Surgery in 2011, the long term revision rate is 6 percent after five years and 12 percent after ten years. You can reduce future problems by maintaining your weight and avoiding activities that can put undue stress on the joint, such as running, jumping, court sports and high impact aerobics.

Despite the high degree of safety and success associated with total knee replacement, it’s important to know the benefits and the risks before undergoing surgery. Only then can you make the right decision.