Knee replacement surgery is now a standard procedure. Though severe complications are rare, it’s a good idea to be aware of the risks before entering the operating room.

Over 790,000 people undergo knee replacement surgery every year in the United States. It’s a common procedure, but complications can develop during and after the procedure.

That said, research also suggests that complications occur in just 7.1% of cases of people under the age of 80. They are more prevalent in older adults over the age of 80 (34.3%).

Read on to learn more about the possible complications during and after knee replacement surgery.

A surgeon may use general or local anesthesia during surgery. It is usually safe, but it can have side effects such as vomiting, dizziness, sore throat, or shivering.

Other possible effects include:

  • breathing difficulties
  • allergic reactions
  • nerve injury

To reduce the chance of problems, be sure to tell your doctor in advance if you take or use any of the following:

  • prescription or over-the-counter medications
  • supplements
  • tobacco
  • recreational drugs or alcohol
  • diabetes medications (including semaglutide (Ozempic), even if you take it off weight loss)
  • blood thinning medications

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 surgery, but they are more common after orthopedic surgeries like knee replacements.

That said, DVT and PE are still relatively rare complications, developing in 0.6-3.0% of knee replacement cases. To reduce the chance of a blood clot after your procedure, your doctor will prescribe a blood thinner following the surgery.

Learn more: Tips to prevent blood clots after 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

That said, infection can still happen, and this can become a severe and life threatening complication, potentially leading to sepsis without immediate treatment.

Some people are more prone to infections as their immune system is compromised by a medical condition or the use of certain medications. Doctors usually give antibiotics during the surgery to lower the chance of infection.

Learn more: How to tell if you have an infection following surgery and what to know about Infections after a knee replacement

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

Complications that can arise include:

  • When a wound is slow to heal, or 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 the fluid.
  • When a Baker’s cyst occurs, 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.

One 2021 study identified a 7% rate of wound complications after total knee replacement, and research suggests they may be more common and more serious after a repeat procedure.

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

This includes people with diabetes and HIV, those who use immunosuppressant medications, and those who take medication following a transplant.

Eating a balanced diet before the procedure that includes a lot of protein, fruit, and vegetables, especially those containing vitamin C, can help your wound heal better afterward.

Learn more about surgical wounds and their complications.

It is normal to have some pain after surgery, but this should improve in time.

Most people recover well from knee replacement surgery and experience an improvement in pain afterward.

The most common complication is that people don’t like the way their new knee works, and in rare cases, pain may persist.

In a 2022 study of 605 people who underwent a total knee replacement procedure, 12% still experienced pain at rest and 38% experienced pain during movement two years after surgery.

Speak with your doctor if you have ongoing or worsening pain.

Learn more: How to manage pain, swelling, and bruising after a total knee replacement.

In rare cases, a person may need a blood transfusion after a knee replacement procedure. Multiple studies suggest the rate of transfusion after knee replacement is often lower at 1-5.1%.

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 people may experience an allergic reaction to the metal used in the artificial knee joint. This is called metal hypersensitivity. Doctors don’t fully understand why it develops, and there isn’t a lot of research to support it as a clear diagnosis yet.

That said, according to a 2019 study, the prevalence of such a reaction among 233 people who underwent a total knee replacement was found to be just over 15%. The most common metal people reacted to was chromium at nearly 12%, followed by nickel at almost 9% and cobalt at about 6%. Implants may contain titanium or a cobalt-chromium-based alloy.

While this isn’t so common, if you already know you have a sensitivity to metal from other exposures, be sure to tell your surgeon. Also, tell them of other allergies you may have before surgery.

According to a 2020 study of 47,585 knee replacement procedures, 0.4% of people experienced nerve palsy, which can mean the loss of sensation in the leg or the inability to hold the leg up (foot drop).

Other types of nerve damage include numbness, weakness, tingling, or 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. In a 2021 study, of 1350 total knee replacement procedures, 33 people, or 2.44%, experienced stiffness after surgery.

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.

Generally, this isn’t so common. More than 82% of replacement knee joints are still working 25 years later, according to figures published in 2018.

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

Learn more: Clinical outcomes and statistics of knee replacement.

What is the most common complication of total knee replacement?

It’s difficult to define the absolute most common complication of total knee replacement because this can vary by hospital and geographic area and can also be influenced by various social and economic factors.

That said, a 2017 study examining a Medicare beneficiary population found that the overall complication rate for knee replacement was 2.09%. In this study, the most common complication type for knee replacements during the procedure was pneumonia at 0.50%, whereas the most common complication after discharge was infection at 0.46%.

Another 2022 study separated complication rates by in-patient vs outpatient procedures. In-patient means the person was hospitalized for the procedure, whereas out-patient means that person could go home that day. Overall, in-patient procedures had more complications than out-patient procedures. In this study, a superficial surgical site infection and urinary tract infection (UTI) were most common for both types of procedures.

Can too much walking damage a knee replacement?

Walking doesn’t necessarily have to damage a knee replacement if you allow your knee to heal and add it to your movement routine gradually in consultation with your doctor.

In general, research suggests you have a lower risk of falling after a joint replacement. That said, older adults have a slightly higher risk. According to a 2018 study, 17.2% of 134 people who had the procedure fell at least once 6 months after surgery. In two-thirds of those cases, the fall occurred while walking.

When you’re ready to walk, begin by using a handrail on stairs, and keep away from messy floors or slippery terrain that may cause you to trip.

Learn more: What exercises (or movements) to avoid after a knee replacement

How do you know if your knee replacement is failing?

Signs of a failing knee replacement can include increased instability or pain, infection, or bone fracture. Sometimes, small pieces of the implant can break off and cause joint inflammation.

Learn more: What is knee replacement revision surgery, and when do you need it?

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.