Knee replacement surgery is now a standard procedure, but you should still be aware of the risks before you enter the operating room.

Over 600,000 people undergo knee replacement surgery every year in the United States. Severe complications, such as an infection, are rare. They occur in fewer than 2 percent of cases.

Relatively few complications happen during the hospital stay after a knee replacement.

Healthline analyzed data on over 1.5 million Medicare and privately insured people to take a closer look. They found that 4.5 percent of people who are aged under 65 experience complications while in the hospital after a knee replacement.

For older adults, however, the risk of complications was more than double.

  • About 1 percent of people develop an infection after surgery.
  • Fewer than 2 percent of people develop blood clots.

In rare cases, a person may have osteolysis. This is inflammation that occurs due to microscopic wear of the plastic in the knee implant. The inflammation causes bone to essentially dissolve and weaken.

A surgeon may use general or local anesthesia during surgery. It is usually safe, but it can have adverse effects.

The most common side effects include:

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

Other possible effects include:

  • breathing difficulties
  • allergic reactions
  • nerve injury

To reduce the risk of problems, be sure to tell your doctor in advance about any of the following:

  • prescription or over-the-counter medications
  • supplements
  • tobacco use
  • use or recreational drugs or alcohol

These can interact with medications and may interfere with anesthesia.

There is a risk of developing a blood clot after surgery such as deep vein thrombosis (DVT).

If a clot travels through the bloodstream and causes a blockage in the lungs, a pulmonary embolism (PE) may result. This can be life-threatening.

Blood clots can occur during or after any type of surgery, but they are more common after orthopedic surgeries like knee replacements.

Symptoms usually appear within 2 weeks of surgery, but clots can form within a few hours or even during the procedure.

If you develop a clot, you may need to spend extra time in the hospital.

Healthline’s analysis of Medicare and private pay claims data found that:

  • Fewer than 3 percent of people reported DVT during their hospital stay.
  • Fewer than 4 percent reported DVT within 90 days of surgery.

Clots that form and remain in the legs pose a relatively minor risk. However, a clot that dislodges and travels through the body to the heart or lungs can cause serious complications.

Measures that can reduce the risk include:

  • Blood-thinning medications. Your doctor may prescribe medications like warfarin (Coumadin), heparin, enoxaparin (Lovenox), fondaparinux (Arixtra), or aspirin to reduce the risk of clots after surgery.
  • Techniques to improve circulation. Support stockings, lower leg exercises, calf pumps, or raising your legs can boost 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.

If you notice the following in a specific area of your leg, it may be a sign of a DVT:

  • redness
  • swelling
  • pain
  • warmth

If the following symptoms occur, it may mean that a clot has reached the lungs:

  • difficulty breathing
  • dizziness and faintness
  • rapid heartbeat
  • a mild fever
  • a cough, which may or may not produce blood

Let your doctor know at once if you notice any of these changes.

Ways of preventing blood clots include:

  • keeping the legs raised
  • taking any medication the doctor recommends
  • avoiding sitting still for too long

Infections are rare after knee replacement surgery, but they can occur. Infection is a severe complication, and it needs immediate medical attention.

According to Healthline’s analysis of Medicare and private pay claims data, 1.8 percent reported an infection within 90 days of surgery.

Infection can occur if bacteria enter the knee joint during or after surgery.

Healthcare providers reduce this risk by:

  • ensuring a sterile environment in the operating room
  • using only sterilized equipment and implants
  • prescribing antibiotics before, during, and after surgery

Ways of preventing or managing infection include:

  • taking any antibiotics the doctor prescribes
  • following all instructions about keeping the wound clean
  • contacting the doctor if there are signs of infection, such as redness, soreness, or swelling that get worse rather than better
  • making sure the doctor knows about any other health conditions you may have or medications you are taking

Some people are more prone to infections as their immune system is compromised by a medical condition or the use of certain medications. This includes people with diabetes, HIV, those who use immunosuppressant medications, and those who take medication following a transplant.

Find out more about how infection happens after knee replacement surgery and what to do if it does.

It is normal to have some pain after surgery, but this should improve in time. Doctors can provide pain relief until this happens.

In rare cases, pain may persist. People who have ongoing or worsening pain should seek advice from their doctor, as there may be a complication.

The most common complication is that people don’t like the way their knee works or they continue to have pain or stiffness.

In rare cases, a person may need a blood transfusion after a knee replacement procedure.

Blood banks in the United States screen all blood for possible infections. There should not be any risk of complications due to a transfusion.

Some hospitals ask you to bank your own blood before surgery. Your surgeon may advise you on this before the procedure.

Some people may experience a reaction to the metal used in the artificial knee joint.

Implants may contain titanium or a cobalt-chromium-based alloy. Most people with a metal allergy already know they have one.

Be sure to tell your surgeon about this or any other allergies you may have well before surgery.

The surgeon will use sutures or staples used to close the wound. They typically remove these after about 2 weeks.

Complications that can arise include:

  • When a wound is slow to heal and bleeding continues for several days.
  • When blood thinners, which can help prevent clots, contribute to bleeding problems. The surgeon might need to reopen the wound and drain fluid.
  • When a Baker’s cyst occurs, when fluid builds up behind the knee. A healthcare professional may need to drain the fluid with a needle.
  • If the skin does not heal properly, you might need a skin graft.

To reduce the risk of problems, monitor the wound and inform your doctor if it is not healing or if it continues to bleed.

The major arteries of the leg are directly behind the knee. For this reason, there’s a very small chance of damage to these vessels.

A vascular surgeon can usually repair the arteries if there is damage.

Up to 10 percent of people may experience nerve damage during surgery. If this happens, you may experience:

  • numbness
  • foot drop
  • weakness
  • tingling
  • a burning or prickling sensation

If you notice these symptoms, contact your doctor. Treatment will depend on the extent of the damage.

Scar tissue or other complications can sometimes affect motion in the knee. Special exercises or physical therapy can help resolve this.

If there is severe stiffness, the person may need a follow-up procedure to break up the scar tissue or adjust the prosthesis inside the knee.

If there is no additional problem, ways of preventing stiffness include getting regular exercise and telling your doctor if stiffness does not reduce in time.

Sometimes, there may be a problem with the implant. For example:

  • The knee may not bend properly.
  • The implant might become loose or unstable over time.
  • Parts of the implant may break or wear out.

According to Healthline’s analysis of Medicare and private pay claims data, only 0.7 percent of people experience mechanical complications during their hospital stay, but problems can still arise during the weeks after surgery.

If these problems occur, the person may need a follow-up procedure, or revision, to fix the problem.

Other reasons why a revision might be necessary include:

  • infection
  • continued pain
  • knee stiffness

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

Some research suggests that long-term wear and loosening of the implant affects 6 percent of people after 5 years and 12 percent after 10 years.

Overall, more than 82 percent of replacement knee joints are still working 25 years later, according to figures published in 2018.

Ways to reduce wear and tear and the risk of damage include:

  • maintaining a healthy weight
  • avoiding high-impact activities, such as running and jumping, as these can put stress on the joint

Total knee replacement is a standard procedure that thousands of people undergo every year. Many of them have no complications.

It is essential to know what the risks are and how to spot the signs of a complication.

This will help you make an informed decision about whether to go ahead. It will also equip you to take action if a problem does arise.