Knee replacement surgery has become a routine surgery and is the most common type of joint replacement in the U.S. More than 600,000 people each year receive this life-improving surgery and are able to enjoy richer, more active lives free of chronic knee pain.
Most knee replacement patients tend to be older than 50 and have arthritic joints. However, an increasing number of younger people are also replacing their knees because of injury from high-impact sports and activities that wear out their knees quickly. Researchers have found that 94 percent of knee replacements last five years and 88 percent last for 10 years or more.
As more advanced surgical procedures and a wider variety of medical devices become available, people have more choices for treatment. Computer-assisted surgeries and minimally invasive procedures increase the accuracy of the surgery and decrease recovery time. Knee implant manufacturers are already marketing robot-assisted surgical devices and Zimmer-Biomet has floated the idea of partnering with major medical centers to develop on-site 3D printing systems that can generate knee implants customized for individual patients in a matter of hours.
More advanced implants allow for improved joint function. However, in the rush to release new devices to keep up with growing demand, manufacturers may put products on the market that are poorly designed. This may lead to device failure and costly revision surgeries. While the benefits of knee replacement are well recognized, complications from the procedure or from implant failure are also well documented.
Knee Replacement Complications
The American Academy of Orthopedic Surgeons (AAOS) estimates serious complications requiring additional hospitalization or resulting in life-threatening conditions occur in less than 2 percent of all knee replacement surgeries.
Medicare found higher rates among patients it covers. The federal program tracks treatment of its patients 65 and older who have knee replacement surgery and had found that about 5 percent of its patients who receive knee implants develop complications requiring a return to the hospital within 30 days of surgery.
Did You Know
The most serious knee replacement complications include infection and faulty knee implants.
The risk of complications from knee replacement surgery may be greater depending on a person’s age and overall health. Complications can also be the result of general surgical risks, such as a reaction to anesthesia, or problems that develop after surgery and recovery, such as those caused by a faulty implant. The most serious complications include infection and implant failure.
A 2017 study found a higher complication rate for outpatient knee replacement. Researchers looked at an insurance database for patients who had total knee replacement. The database covered surgeries over an eight year period. About 4,400 people had outpatient knee replacements. Another 129,000 stayed a day or two in the hospital after surgery. Those who had outpatient surgery were 28 percent more likely to experience pain and stiffness.
Infection is a risk of any surgery. It occurs in about one in every 50 knee replacements and needs to be addressed as quickly as possible. Patients are given antibiotics for 24 hours after surgery to reduce the chance of infection.
Implant failure can happen years after surgery. It may involve a defect in an individual implant or a design flaw affecting hundreds or thousands of devices. These problems can lead to the implant breaking or loosening.
Knee Replacement Clicking or Popping
It is normal to hear clicking or popping sounds after knee replacement surgery. Most patients experience this with new implants. The noise may be from the metal or plastic parts. Or it may be tendons adjusting to the new implant. The sounds usually decrease or even go away after several months. Patients concerned with clicking should talk to their surgeon. A doctor can tell if the sound is normal or a sign of a complication.
Clicking, by itself, is not a serious problem. But it can be if other conditions happen with it. Patients should let their doctor know if they experience pain along with the clicking. They should also talk with their doctor if swelling accompanies the sounds.
Patients should also let their doctor know if they hear new noises.
Knee Implant Loosening and Faulty Implant Designs
When a knee device fails — by not performing as designed — unsuspecting people are subjected to painful complications. Knee device failure can be the result of a patient being obese or performing excessive high-impact activities.
Sometimes, the device fails because of the manufacturer’s faulty design. The Food and Drug Administration’s 510(k) premarket program allows manufacturers to release knee implants without testing as long as they are similar to products already on the market.
Complications from faulty knee implants may result in the need for a second operation to fix or replace the problematic device.
Unfortunately, many patients and their doctors are unaware of device problems until after they have already been implanted. Complications resulting from a device are tracked by the FDA and labeled as “adverse events.” These complications often result in the need for a second operation, known as revision surgery, to fix or replace the problematic device.
If there are multiple reports of the same problem with a particular model of implant or one of its components, manufacturers will sometimes recall the device. Consumer Union found that between 2003 and 2013, the six largest manufacturers of knee implants issued a total of 709 recalls for their devices.
Loosening is one of the most common complications resulting from a faulty device. This occurs when components of an implant begin to separate from the bone. Soft tissue instead of bone can grow between the components and the bones, creating instability and pain in the joint. Loosening is natural over time, but it usually does not occur for several years. In poorly designed devices, it can occur in a year or less. Infection can also lead to an implant loosing.
Some manufacturers like Zimmer (now Zimmer-Biomet) have blamed device failure on surgeons, despite the fact that one of its NexGen knee implant models showed higher than normal loosening rates – as many as 36 percent of the devices showed loosening within two years. Thousands of people have had Zimmer’s NexGen Knee models implanted since 2002. According to the FDA, there have been hundreds of adverse events resulting from Zimmer’s devices.
Complications from faulty implants include:
- Loosening or fracture of the device components
- Joint instability and dislocation
- Component misalignment and breakdown
- Nerve damage
- Bone fracture
- Swelling and joint pain
Zimmer’s NexGen CR-Flex uncemented knee was designed to encourage the patient’s bone to grow and naturally fuse with the device. Instead, in just a year, the components can loosen and cause a patient severe discomfort and pain.
Infection After Knee Replacement
Not all knee implant complications occur as a result of defective devices. One of the most serious complications of knee replacement surgery is infection.
Fortunately, the chance of having an infected knee prosthesis is relatively low. About 14,000 cases a year — or roughly 2 percent — can lead to painful infections, according to the nonprofit organization Consumer Reports. These infections can be incredibly costly and difficult to treat, and a patient may experience more pain and be more disabled than they were before the original (primary) knee replacement surgery as a result.
Diabetes or rheumatoid arthritis can increase a patient’s risk of infection. Researchers believe this may be due to how the conditions affect their immune systems.
The chance of developing an infection after a knee replacement can vary significantly depending on the hospital where the surgery takes place, according to Doris Peter, director of the Consumer Reports Health Ratings Center. The center found striking differences regarding the amount of reported knee replacement infections among hospitals in the same area.
Additionally, people who undergo revision surgery have a higher risk of developing an infection.
How Do Infections Occur?
Typically, when a microorganism enters a part of the body, the body’s defenses can travel to the site through the blood supply and any medicines can also circulate through the blood to kill bacteria.
Because the knee implant does not have its own blood supply, it is easier for microorganisms to attach to the device and infect surrounding tissues. The surfaces of the implant components are ideal for organisms to adhere to and multiply. Once they multiply, they create a film that acts like a biological shield and protects them from antibiotics.
Although rare, the risk of infection continues for as long as the prosthesis remains in the body. Prosthetic joint infections are classified into three types based on the amount of time that has elapsed from the surgery to the onset of infection.
The three types of infections are:
- Early infections – Occur within 3 months of surgery and are usually caused by microorganisms that enter the body during the operation. People with these infections may suffer from a leaking wound, fever, swelling and effusion (an escape of fluid) around the implant.
- Delayed infections – Can occur from 3 months to 12 months after the surgery and are also caused by organisms entering the body during the surgery. The symptoms of these infections are usually the same as those seen in early infections.
- Late infections – Occur more than a year after surgery. These infections are usually haematogenous, meaning they are acquired from another location in the body. Bacteria from other infections such as a dental infection, pneumonia, skin infection or urinary tract infection can travel in the blood and adhere to the prosthesis. To prevent these types of infections, doctors recommend that patients with prostheses take antibiotics before any surgical procedure. In late infections, joint pain and effusion are common symptoms. Sometimes, the joint is also inflamed, and sepsis — a life-threatening illness caused by the body’s response to infection — may set in.
Doctors test for infections using blood tests, radiology tests, blood cultures and joint aspirations (removing fluid from a joint). The type of bacteria that is present in the infection is tested by culturing the sample in a lab.
Treatment for an Infected Knee Joint
Most treatment strategies for infected knee joints are a combination of surgical procedures and antibiotic therapy. In severe cases, amputation, joint fusion or removal and a two-stage revision surgery may be necessary.
Patients who are not candidates for a second surgery are usually treated with long-term antibiotics to prevent infection. Two-stage revision surgeries have good results in treating infections, though they can be extremely taxing on the body.
These stages are:
- First Stage – In the first stage, the infected prosthetic is removed and cleaned. The wound is also treated with antibiotics. Cement spacers with antibiotics are placed where the infected joint was, and the wound is closed. The patient is immobile for a long length of time while the infection resolves.
- Second Stage – Once the infection has been eradicated, a second-stage surgery is used to re-implant the clean device. Extensive physical therapy usually follows this procedure.
In very rare cases, the infection cannot be treated by revision surgery or antibiotics and reoccurs. Doctors may be forced to amputate a limb in these instances.
However, a procedure called intramedullary arthrodesis of the knee may prevent such a drastic measure. In this procedure, the femur and tibia are fused together by inserting a metal rod into the bones. While the patient avoids amputation, there is significant loss of motion and possible shortening of the leg.
Complications Specific to an Individual’s Surgery
Complications from knee replacements can arise from three different areas: risks that are common to all types of surgery, problems that arise after surgery – even years later – and from the particular circumstances of an individual patient’s knee replacement procedure.
A patient’s individual health, age or physiology can affect his or her particular risk of complications. Osteoporosis or other bone conditions may increase the risk for fractures or problems with bones adhering to the implant. An analysis of patient records also found those patients over 70, those with BMI of 30 or more and patients with a pre-existing pulmonary disorder were at greater risk of various complications.
Difficulty during surgery also may lead to unintended damage to nerves, arteries or ligaments.
The most common complications based on individual surgeries include broken bones, damaged nerves, arteries and ligaments, and an individual’s allergic or immune reactions to the implant’s components.
Complications Specific to an Individual’s Surgery Include:
- Metal Allergies – Metals used in knee implants are usually titanium or an alloy of cobalt and chromium. These metals are chosen for their durability and because the body will not reject them. But people with metal allergies may have severe reactions and should let their doctor know when first discussing knee replacement.
- Bone Fractures – Knee implants require removing bone and attaching components to the thighbone and tibia, one of the lower leg bones. In rare cases, a bone may fracture during surgery. In other rare cases, the bone that has been cut may not heal properly or in a way that affects the implant.
- Ligament Damage or Instability – Less than 1 percent of knee replacement patients suffer ligament damage during knee replacement surgery. When ligaments are cut, damaged or improperly balanced during or after surgery, the knee can become unstable. Since most knee implants are intended to work with a patient’s existing ligaments, if they are damaged, the implant may not move correctly.
This can cause the knee to give way, usually from side to side. This typically improves over time after the ligaments heal, but occasionally a knee brace may be required to prevent buckling after surgery.
- Nerve or Artery Damage – Fewer than 1 in a thousand patients suffer artery damage during knee replacement surgery and less than 1 percent of patients suffer nerve damage. Major arteries run behind the knee and there is a slight risk these may be damaged during knee replacement surgery. A surgeon can usually repair any damage. Nerve damage is also low risk, but patients may feel numbness in the leg or foot following surgery. Numbness usually corrects on its own during the healing process, but it may take months.
- Osteolysis (Immune System Reaction) – Osteolysis is a complication that occurs when plastic components of the implant generate and spread tiny plastic particles. These particles activate the body’s immune defenses, including white blood cells. The white blood cells digest these foreign particles, but they also can digest bone.
The result is bone damage and implant loosening. This condition is more common in implants that are made of polyethylene. While this material allows for more natural joint function, it is also more susceptible to wear. When severe bone loss occurs, the implant loosens and revision surgery is required.
Complications of Surgery in General
Any type of surgery can be traumatic to the body and poses general complications. A 2015 study by Harvard University researchers found about 6 percent of general surgery patients had to be readmitted to the hospital following their procedure.
Although infection is the leading general surgery complication, other complications can include reaction to anesthesia, life-threatening blood clots, and rarely, heart or cardiovascular complications.
Reaction to Anesthesia
Death due to a reaction to anesthesia is extremely rare – less than 1 in 100,000 patients die from a reaction to anesthesia.
In the most serious reactions, cognitive dysfunction or memory loss may affect as many as 12 percent of patients over 60. People with heart or lung disease, Alzheimer’s, Parkinson’s or who have had a stroke are at greatest risk of permanent memory loss.
Delirium or confusion upon waking up from anesthesia can affect up to 70 percent of people 60 or older. It may recur but usually clears up in a week.
The most common reactions to anesthesia are minor and can be easily treated:
- Shivering or chills during recovery after surgery can occur as the body cools down. This affects up to half of all patients.
- A sore throat or hoarseness from the breathing tube affects about 40 percent of patients.
- Nausea and vomiting can occur for the first few days after any surgery. This affects 20 to 30 percent of patients.
- Dental trauma, usually to the front teeth, happens in only about 1 in every 2,000 patients.
Blood clotting is a natural healing process in the body and surgery can trigger a clotting response. In some cases, blood clots can pose a serious health problem. Clots forming in the lower legs can cause a condition called deep vein thrombosis (DVT). If these clots break free, they can travel to the lungs and cause a life-threatening condition called a pulmonary embolism (PE).
An analysis of Medicare and private insurance records found DVT occurs in fewer than 3 percent of surgical patients in the hospital, and fewer than 4 percent of patients within 90 days of surgery. But it is estimated that as many as 50 to 70 percent of knee replacement patients may develop DVT without showing any symptoms. Other studies have found that older patients are at greater risk of DVT and death following knee replacement surgery.
Blood Loss and Wound Complications
Hematomas occur when blood leaks and collects under the skin. This may resolve on its own, but if it does not, minor surgery may be required to remove the blood. Aspirin or antibiotics can increase the risk of hematomas. A fluid buildup called a “Baker’s Cyst” can form behind the knee that may require draining with a needle.
Sutures are usually removed after two weeks, but may be delayed by slow healing. Damage to the skin around the wound may also require a skin graft in rare cases.
Stroke or Heart Failure
Strokes complications are extremely rare following surgery. Patients with kidney or blood pressure conditions are more likely to experience a stroke. Blood thinners can reduce the likelihood. Less than one percent of people without a preexisting heart condition experience heart failure due to surgery.
Hyperglycemia (high blood sugar)
Hyperglycemia is an excess of glucose in the blood and is usually associated with diabetes. Paradoxically, people without diabetes are more likely than those with the condition to experience high blood sugar after surgery. Researchers have found hyperglycemia following surgery may be a reaction to infection at the surgical site. Overall, high blood sugar is a rare complication.
Blood Transfusion Allergies
The need for blood transfusions during knee replacement surgery is rare, and allergies to blood transfusions are rare among those patients who require them. Among the people most at risk of needing a transfusion during or after surgery are patients who have anemia. Preparation in the days and weeks ahead of the procedure can reduce the chances for a transfusion. Allergies can happen even if the blood type matches the patient’s. Blood allergies usually present as itching and hives and can be treated in most cases with antihistamines.
Complications That Can Happen After Knee Replacement
Some complications that occur during knee replacement surgery may not show up until after the procedure. These can begin while the patient is recovering in the hospital while other complications can take years to occur.
A 2015 review of more than 1.5 million patients – insured through Medicare or private insurers – found 4.5 percent of knee replacement patients under the age of 65 suffered complications while hospitalized. The rate doubled for people 65 and older. About 1 percent reported infections and fewer than 2 percent experienced blood clots as the most common complication during hospital recovery.
In addition to general post-surgery complications, there are several that are specific to knee replacements. In addition to implant failure, these can include joint stiffness, issues with the kneecap, skin conditions, pain and fractures near the implant.
Complications that can happen after knee replacement surgery include:
- Arthrofibrosis (Joint Stiffness) – Patients who have knee replacement surgery are susceptible to significant joint stiffness, known as arthrofibrosis. If the person is obese, has diabetes or is slow to mobilize after surgery, it can worsen this condition.
This usually happens when excessive scar tissue builds up around the joint. Exercise can resolve many stiffness issues but pain may prevent patients from exercising adequately. In some cases, doctors may treat joint stiffness by administering an anesthetic to the knee and manipulating it to break down the scar tissue. When the scar tissue is extensive, another surgery may be required to remove it.Less than 1 percent of patients with this complication will require revision surgery to correct the problem.
- Extensor Mechanism Disruption – Extensor mechanism disruption is one of the most serious mechanical complications that can occur after knee replacement. This occurs when the tendon attached to the patella (kneecap) moves away from the tibia during or after surgery. When this happens, the knee cannot extend. Surgery is required to repair the tendon, and a tendon graft may be required.
- Fractures near the Implant – Bones can fracture near the implant and usually occur from a fall. Osteoporosis can contribute to the risk of fractures. Patients usually require another surgery to repair broken bones or to replace parts of their implant.
- Pain – While most pain steadily diminishes following surgery, 10 to 20 percent of knee replacement patients report moderate to severe long-term pain. Revision surgery may not resolve this issue and patients may have to seek some form of pain management care.
- Patella Tracking Problems – A healthy patella (kneecap) glides up and down in a groove over the femur. Sometimes the patella dislocates after surgery. This is most commonly associated with kneecaps that have been resurfaced with a plastic button, which can cause the patella to track differently or catch and “clunk” as it passes over the metal flange of the knee. In some cases, the tracking problem is severe enough to warrant revision surgery.
- Skin and Scarring Complications – The surgical scar can remain painful or the skin around the scar can remain numb for months following surgery. In rare cases, the wound may not fully heal.
Complications from Revision Surgery
Revision surgery to replace a previously implanted artificial knee includes all the same risks of complications as the primary surgery – and the chances of complications increase. At the same time, revision surgery is more complicated than the original procedure and is not expected to last as long as the original replacement. Hospital stays for patients are also longer for revision surgeries.
In most cases, patients or their insurance provider have to pay for the revision surgery, not the manufacturer of the knee implant.
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. Surgeons perform about 54,000 revision surgeries for knee implants every year in the U.S., about half happen within two years of the primary surgery.
The most common reason for revision surgery in the short term is to address an infection. In the long term, revision surgery may be necessary to correct complications including dislocations, fractures, pain, joint stiffness, loosening of the device or some other device failure.
About 1 in 50 knee replacement patients may require revision surgery five years after their primary surgery. The rate is about 12 percent after 10 years. The chance of needing revision surgery also increases with the patient’s age.
The Risk of Death after Knee Replacement
The risk of death from knee replacement is very low, but it does occur. The 30-day mortality rate for a total knee replacement is about 1 in 400 or 0.25 percent, according to the American Academy of Orthopaedic Surgeons.
In a 2012 study published in The Bone & Joint Journal, researchers in the U.K. analyzed nearly 2,500 people who underwent total knee replacement over a 10-year span, with predicted life expectancy based on age and gender factored in.
A 2012 study found that mortality rates were the highest in the 30 to 90 days following surgery.
The study found that mortality rates were the highest in the 30 to 90 days following surgery, with 99 percent of patients surviving at least one year, 90 percent surviving at least five years and 84 percent still living after 10 years.
Improvements in surgical techniques and growing experience among surgeons have been lowering the risk of death as more knee replacements are performed. A 2014 study in the British journal The Lancet looked at more than 467,000 primary knee replacement outcomes over an eight year period in the UK and concluded post-operative death rates had “fallen substantially.”
Please seek the advice of a medical professional before making health care decisions.
Kristin Compton is a medical writer with a background in legal studies. She has experience working in law firms as a paralegal and legal writer. She also has worked in journalism and marketing. She’s published numerous articles in a northwest Florida-based newspaper and lifestyle/entertainment magazine, as well as worked as a ghost writer on blog posts published online by a Central Florida law firm in the health law niche. As a patient herself, and an advocate, Kristin is passionate about “being a voice” for others.