September 19, 2022

8 Little-Known Dangers of Knee Replacement Surgery

Knee replacement surgery may provide an often effective pathway to improving joint pain and mobility for many, but they are not without their risks…

If you’ve been dealing with the chronic pain and limited mobility typical of osteoarthritis, chances are knee replacement surgery has crossed your mind. The Agency for Healthcare Research and Quality (AHRF) reports over 600,000 knee replacement surgeries are performed each year  in the U.S., with osteoarthritis (OA) being a primary driver for surgery [1].

Knee replacement surgery, also known as knee arthroplasty, is generally viewed as a last resort when pain, mobility, and stiffness in the knee joint begin to severely impact your ability to function. Why? Because the surgery can often be accompanied by a range of side effects, from long-lasting persistent knee pain to infection and more. 

What are Knee Replacement Surgeries? 

Knee replacement is an operation where doctors surgically remove the damaged cartilage and bone in the joint and insert a prosthetic joint. A total knee arthroplasty involves removing and replacing the entire joint, whereas a partial knee replacement may only require exchanging a few compartments of the joint. If two or more of the four main joint compartments are damaged, most doctors will advise total knee replacement surgery.

The American Academy of Orthopedic Surgeons (AAOS) reports that 90% of knee replacement patients experience improvements in pain and in their daily ability to function [2]. 

However, of those 600,000 knee replacement surgeries each year, complications occur in about 5% of patients, with another 1 in 20 patients needing additional surgery after about 12 years [3]. While many of these complications are mild and resolved swiftly, in rare cases complications may be severe and potentially life threatening.

Who is Eligible for Knee Replacement Surgery?

Most knee replacement patients are between 55-75 years old, although eligibility is assessed on a case-by-case basis. Knee replacement surgery is advised as a last resort, when other non-operative measures like corticosteroid injections, physical therapy, medications, supplements, bracing, and alternative methods have been exhausted.

When chronic arthritis pain and mobility limitations begin severely impacting your quality of life, that’s when physicians may consider knee replacement surgery the best course of action.

Otherwise, the factors that guide eligibility for joint replacement surgery include:

  • Pre-existing infection. Surgery will not be an option until the infection has fully healed.

  • Smoking cigarettes. This won’t make you ineligible, but could be a deciding factor if you’re on the edge of eligibility. Research suggests smokers are 50% more likely to experience complications during surgery than non-smokers [4].

  • Severe osteoporosis. Mild and moderate cases of osteoporosis (a disease characterized by bones growing progressively more brittle and prone to fractures) can impact surgery procedures. Severe osteoporosis may make the surrounding bones too brittle to support the new prosthetic joint.

  • Obesity. Obesity doesn’t make one ineligible, but if weight impairs your ability to move, say in standing up, you may not be able to participate in the post-surgery physical therapy which is so critical to seeing long-term beneficial results.

  • Substance abuse, alcoholism, mental illness. Preventing falls and ensuring adherence to post-op rehabilitation are critical to maximize post-surgery results. So while these factors don’t make someone ineligible, a doctor will want to know there’s a plan in place so they don’t impact rehabilitation.

  • Age. Because knee joint prosthetics have a limited lifespan, most physicians advise delaying surgery as long as possible to reduce the need for follow-up joint surgeries in the future. For this reason, a younger age can make osteoarthritis patients ineligible for knee replacement surgeries.

How Long Do Knee Replacements Last?

Daily wear and tear takes its toll on even the most advanced metal and plastic joint replacement parts. If you’re thinking about knee arthroplasty, it’s important to consider the average lifespan of a knee joint prosthetic.

The AAOS reports that over 90% of knee replacements are still functioning after 15 years, with the general lifespan of knee prosthetics ranging 10-15 years [5]. However, this number can be somewhat deceiving… 

Revision Surgery

Research published in The Journal of Bone and Joint Surgery found that both hip and knee replacement surgeries had a revision rate of roughly 6.3% within the first five years, and 12% after ten years [6]. Another study of 55,000 knee replacement patients reports revisions more conservatively, finding 3.9%-5% needed revision surgery within 10 years and 10.3% required revision surgery by the 20-year mark [7,8].

However, the length of time a prosthetic lasts depends on how it’s used. If you’re involved in a lot of physical activity that places increased pressure and wear on your knees, your prosthetic may degrade faster.

Revision surgeries may be necessary due to a number of joint replacement complications, including infection, implant failure, osteolysis, persistent pain and stiffness. Revision surgeries are complex and often take more time than primary knee replacement surgeries, leading to more time spent in surgery and higher rates of complications.

Knee Replacement Surgery Complications and Risks

Although severe complications are rare, they do occur. Below are some of the most common sources of knee replacement complications.

Persistent knee pain

Some pain and discomfort is to be expected after joint replacement surgery and should lessen over two to three months. Unfortunately, some knee replacement patients experience long-term, persistent pain. One study found that about 20% of total knee replacement patients experience persistent chronic pain after knee surgery, regardless of the procedure’s quality [9].  Post-surgery pain is often resistant to treatment and may only be resolved through revision surgery, chronic pain medications, or mind-body holistic treatments.


Anesthesia is a type of drug often used during surgery to prevent patients from feeling pain. General anesthetics are used to help a patient remain unconscious during procedures, while regional or localized anesthetics are provided to numb a specific area. The more time a person spends under anesthesia, the higher the risk of potential complications.

Common side effects of anesthesia include drowsiness, dizziness, discomfort, aches, a sore throat, vomiting, and shivering. 

In more rare circumstances, anesthesia can prompt allergic reactions, difficulty breathing, and nerve damage. General anesthesia also increases the risks of blood clots, blood loss, pneumonia, stroke, and heart attacks. While local anesthetics are associated with fewer complications and side effects, they typically aren’t used for total knee replacement surgeries.

Blood Clots

Blood clotting is the body’s natural response to certain types of injuries. If we get a paper cut, our blood clots to stop the bleeding and help the injury heal, ultimately dissolving once the injury has healed. However, when blood clots form inside blood vessels without an injury, that’s when they begin to pose a threat to our health.

A blood clot that occurs in the deep veins in our legs is called deep vein thrombosis (DVT). Because of the blood buildup behind the clots, they often cause swelling and pain. If the clot dislodges it can travel in the bloodstream to more vulnerable parts of the body and block blood flow. This interrupted flow of oxygen and nutrient-rich blood can result in a pulmonary embolism, heart attack, or stroke.

The risk of blood clots increases the longer someone remains stationary during and after surgery, making post-surgery movement and rehabilitation even more essential.

A study of over 1.8 million knee replacement patients found that roughly 1.3% of patients experienced venous thromboembolism (VTE) (an umbrella term that refers to both pulmonary embolisms and deep vein thrombosis). Additionally, patients who developed a pulmonary embolism or DVT experienced a 21-fold increase in their risk of in-hospital mortality [10].


While antibiotics are given throughout and after surgery, infections still occur within 2-3% of knee replacement patients [11]. Most of the time, these infections are easily and swiftly treated with additional antibiotics. In rare cases though, infection may become so severe that it requires removing the replacement joint. If infection is not treated, it can become life-threatening.

Another little known fact – although the risk of infection decreases as the wound heals, people who undergo joint replacement surgeries experience a life-time increased risk of infection. For this reason, joint replacement patients are advised to let their dentists know they’ve had a joint replacement surgery before dental procedures, which is a common pathway to infection.

Nerve or blood vessel damage

While some numbness and stiffness is to be expected post-surgery, prolonged numbness, pain, or impaired movement may be a sign of blood vessel or nerve damage. Often this damage will heal on its own. However, if a blood vessel or nerve was significantly impacted during the surgery, a second surgery may be necessary to repair the damage (although the damage is not always reversible.)

Long-term stiffness

Some stiffness is normal after surgery, as the area is still healing. Most people find that after knee surgery, they’re able to bend their knees at least 115 degrees. However, stiffness that inhibits this range of motion can be caused by scar tissue build-up around the joint. Working with a physical therapist can help prevent and break up accumulating scar tissue to maintain a greater range of motion after surgery.

Stiffness can also result from excess bone that grows around the replacement joint. In this case, additional surgery may be necessary to remove the new bone growth and to free up movement.

Implant failure

Whether made of metal or plastic parts, knee joint prosthetics are built to be long-lasting. That being said, implant failure does occur and can result in persistent pain and stiffness. Failed implants may result from infection and pain, or come loose, lose stability, or wear out over time and require a second, revision therapy to provide relief.


Research suggests osteolysis may be the biggest driver behind implant failure and revision surgeries [12]. Osteolysis, a process that degrades and breaks down bone, may be induced by microscopic plastic particles from the prosthetic that trigger inflammation.

Considering Your Options

Because joint replacement surgery is not without its risks, it’s important to exhaust all your options. Knee arthroplasty is a widely successful procedure, but may not lead to the idyllic pain and stiffness-free living that many hope for when they commit to the surgery.

Some of these alternative non-surgical options include:

  • Exercise (and weight loss, if necessary)

  • Physical therapy

  • Corticosteroid injections into the knee

  • Pain relief medications (e.g., acetaminophen – Tylenol)

  • Non-steroidal anti-inflammatory drugs (e.g., ibuprofen – Motrin, celecoxib – Celebrex, naproxen – Naprosyn)

  • Diet and lifestyle

  • Anti-inflammatory supplements 

  • Energy healing 

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