Can a Knee Replacement Get Infected Years Later?

A knee replacement can get infected years, even decades, after surgery. While most people think of infection as a risk that peaks in the weeks right after an operation, the reality is that an artificial joint remains vulnerable to bacterial colonization for as long as it stays in your body. Registry data covering more than 112,000 primary hip and knee replacements found that late infections, defined as those occurring more than two years after surgery, happened at a rate of about 0.08% per year for knees, and “very late” infections beyond five years still occurred at roughly 0.06% per year.¹ Those numbers sound small in any given year, but they accumulate over a lifetime, and the consequences when infection does strike are serious.

Why an Artificial Joint Stays Vulnerable Indefinitely

Your natural knee joint has a blood supply that feeds living bone and cartilage, bringing immune cells directly to the site of any bacterial threat. An artificial joint is different. Metal, plastic, and cement are not living tissue, so your immune system cannot patrol them the way it patrols the rest of your body. Bacteria that land on these surfaces can attach, multiply, and form a sticky protective layer called a biofilm. Once a biofilm establishes itself, it shields the bacteria from both antibiotics and your immune response, making the infection far harder to treat than a typical skin or urinary infection.

Research has shown that not all implant surfaces attract bacteria equally. In one laboratory study examining the tibial components of knee replacements, the polyethylene (plastic) surfaces harbored about three times more bacteria than the metal surfaces.² Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most common biofilm-forming organisms linked to implant infections, and its resistance to standard antibiotics makes it a particular concern.³ But plenty of other organisms can be involved too, including unusual species that rarely cause problems elsewhere in the body. One published case described a knee prosthesis becoming infected with Staphylococcus xylosus, a species not typically thought of as a human pathogen, a full 18 years after the original surgery.⁴

How Bacteria Reach a Joint Years After Surgery

Early infections, those that show up within weeks of surgery, usually trace back to bacteria introduced during the operation itself. Late infections follow a fundamentally different path. The most common route is called hematogenous seeding: bacteria enter the bloodstream from an infection somewhere else in the body and then settle on the implant surfaces. A dental abscess, a skin infection, a urinary tract infection, or even a bout of pneumonia can release bacteria into the blood, and those organisms have a tendency to home in on foreign material like joint prostheses.⁵

One documented case involved a man whose knee prosthesis became infected after a genital tract infection seeded bacteria through his bloodstream to the implant. Another report in the older literature described a late knee prosthesis infection traced to a urinary tract infection. These examples illustrate a broader principle: any infection that enters the bloodstream can potentially land on your artificial joint. This is why surgeons sometimes prescribe prophylactic antibiotics before dental procedures for patients with joint replacements, though guidelines on this have shifted over the years and vary by country.

A less common but recognized route is direct contamination, for example through a wound near the knee that allows bacteria to reach the implant from outside. There is also ongoing debate about whether some late infections represent low-grade organisms that were present since the original surgery but took years to cause noticeable symptoms, slowly multiplying within a biofilm that kept them hidden from routine detection.

Who Is Most at Risk

Not everyone with a knee replacement faces the same odds of a late infection. A large observational study drawing on registry data from England and Wales identified a range of factors that increase the risk of needing revision surgery because of infection. Several of these are worth knowing about because they are modifiable or at least manageable:

Obesity: People with a body mass index of 30 or above had roughly 50% higher risk compared to those with a BMI under 25.
Diabetes: Diabetes raised the risk by about 40%. A separate meta-analysis looking at over 120,000 knees found that the infection rate after primary knee replacement was 1.9% in people with diabetes compared to 1.2% in those without.⁶
Liver disease: This carried more than double the risk of prosthetic joint infection.
Previous joint infection: Having had septic arthritis before the replacement was the single strongest predictor, increasing risk nearly fivefold.
Male sex: Men had about 80% higher risk than women.
Younger age: Counterintuitively, patients under 60 had higher infection rates than those over 80, possibly because younger patients are more physically active and place greater mechanical stress on the joint.

Chronic lung disease, peripheral vascular disease, rheumatic and connective tissue disorders, and inflammatory arthropathies also elevated the risk.⁷ In practical terms, if you have a knee replacement and also live with one or more of these conditions, paying attention to any new knee symptoms and managing your underlying health is especially important.

What a Late Infection Feels and Looks Like

Late prosthetic joint infections often present differently from early ones. An early infection tends to be dramatic: redness, warmth, swelling, wound drainage, and fever within days or weeks of surgery. A late infection, by contrast, can be subtle. The hallmark is usually a gradual onset of increasing pain in a knee that had been functioning well for years. The pain may come with stiffness, mild swelling, or a feeling that the joint just is not right anymore. Fever and obvious redness are less common in late infections, which makes them easy to confuse with other problems.

The main condition that mimics a late infection is aseptic loosening, where the implant gradually loses its bond with the surrounding bone for mechanical rather than infectious reasons. Both conditions cause pain that worsens over time, and both can show changes on X-rays. Distinguishing between the two matters enormously because the treatments are completely different. Advanced imaging techniques are being explored to improve this distinction. One study evaluated a specialized PET/CT scan using a gallium-based tracer and found that combining it with another type of bone scan improved the ability to correctly identify infected joints, reaching sensitivity above 95%.⁸

In most cases, though, the diagnosis starts with blood tests looking for markers of inflammation, followed by a needle aspiration of fluid from the knee. That fluid gets sent for cell counts, cultures, and increasingly for newer biomarker tests. One biomarker called alpha-defensin, a small protein produced by white blood cells fighting infection, has emerged as a particularly useful diagnostic tool. A systematic review and meta-analysis found it had pooled sensitivity and specificity both above 97% for identifying prosthetic joint infection.⁹ That said, another study looking at real-world clinical use found somewhat lower performance, with sensitivity and specificity both around 82%, suggesting the test works best as one piece of evidence rather than a standalone diagnostic answer.¹⁰

Treatment When Infection Arrives Late

Treating an infected knee replacement is far more involved than a course of antibiotics. The approach depends on several factors: how long the infection has been present, what organism is causing it, how well-fixed the implant is, and the patient’s overall health. There are essentially three surgical strategies, ranging from least to most invasive.

The least disruptive option is called DAIR, which stands for debridement, antibiotics, and implant retention. The surgeon opens the knee, cleans out infected tissue, washes the joint thoroughly, and replaces any exchangeable components like the plastic liner, while leaving the main metal implants in place. This is followed by weeks of antibiotics. DAIR works best when the infection is caught early and the implant is still well-fixed. For late chronic infections, the success rate drops. Key factors that predict failure include having a draining sinus tract, infection with resistant Staphylococcus species, a compromised immune system, and delays between symptom onset and surgery.¹¹ Some surgeons add local antibiotic delivery through a calcium sulfate matrix packed into the joint, which releases antibiotics directly at the site of infection.¹²

For most late infections, though, the standard treatment is a two-stage revision. In the first surgery, the entire prosthesis and all cement are removed, the joint is thoroughly cleaned, and a temporary antibiotic-loaded cement spacer is implanted. The patient then undergoes six to twelve weeks of targeted antibiotic therapy. Once blood markers confirm the infection is controlled, a second surgery removes the spacer and implants a new knee prosthesis.¹³ This approach is widely considered the gold standard for chronic prosthetic joint infections, and the reported success rate for eradicating infection runs between 88% and 96%.¹⁴

The two-stage revision is grueling for patients. You are essentially living without a functioning knee for weeks to months between stages, often with limited mobility and sometimes significant pain. And even with high success rates, a meaningful minority of patients face recurrent infection. One long-term study found that when a second two-stage revision was needed because the first failed, infection was successfully controlled in about 78% of those cases. Among the remaining patients who needed yet a third attempt, 75% achieved infection control. The long-term survivorship of the final implant, free of removal for recurrent infection, was about 94% at fifteen years.¹⁵

In the most severe cases, where repeated surgeries fail to control infection or the patient cannot tolerate further procedures, the remaining options are permanent removal of the prosthesis (leaving what is called an arthrodesis, or fused joint, or sometimes a resection arthroplasty with no implant at all) or, in extreme circumstances, amputation. These outcomes are rare but real, and they underscore why prevention and early detection matter so much.

The Financial Weight of a Late Infection

The cost of treating a prosthetic joint infection dwarfs the cost of the original knee replacement. One study found that managing an infected knee implant required three to four times the hospital and surgeon resources of a primary knee replacement, and about twice the resources of a standard revision for non-infectious reasons. Hospitals in that analysis experienced an estimated net loss of around $30,000 per Medicare patient treated for prosthetic joint infection.¹⁶ A study from Pakistan found that the total cost of managing a prosthetic joint infection was about 4.5 times higher than an uneventful primary knee replacement.¹⁷

At a population level, the numbers are staggering. In the United States, the total annual cost of prosthetic joint infections has risen from roughly $167 million in 2002 to an estimated $385 million by 2017, and projections suggest it could reach $753 million annually by 2030.¹⁸ These costs reflect not just the surgeries themselves but the prolonged hospital stays, extended courses of expensive intravenous antibiotics, rehabilitation, and the time patients spend unable to work. For an individual patient, the estimated lifetime cost of treatment has been put at roughly $390,000.

Practical Steps to Reduce Your Risk

You cannot eliminate the risk of a late infection entirely, but you can meaningfully lower it. Several of the strongest risk factors are things you can influence or manage with your doctor’s help.

Keeping blood sugar well-controlled if you have diabetes is one of the most impactful things you can do. The data consistently show that diabetes raises infection risk, and poorly controlled blood sugar impairs your immune system’s ability to fight off bacteria. Managing your weight has a similar dual benefit: it reduces mechanical stress on the implant and improves immune function. If you smoke, stopping matters too, since smoking impairs wound healing and immune surveillance, even years after the original surgery.

Be vigilant about infections elsewhere in your body. A urinary tract infection, a tooth abscess, a skin wound that is not healing properly: any of these can seed bacteria into your bloodstream. Treat them promptly rather than waiting them out. Let your doctor know you have a joint replacement whenever you are being treated for any infection, as they may choose to be more aggressive with antibiotics to prevent seeding.

The question of prophylactic antibiotics before dental work has been debated for years. Current guidelines from the American Dental Association and the American Academy of Orthopaedic Surgeons generally do not recommend routine antibiotic prophylaxis for most dental procedures in joint replacement patients. However, individual surgeons may still recommend it for patients with additional risk factors, so it is worth having a direct conversation with both your surgeon and your dentist.

Pay attention to your knee. If a knee that has been doing well for years starts hurting, swelling, or feeling unstable without a clear mechanical explanation, do not assume it is just aging or wear. Mention to your doctor that you have an artificial joint and ask whether infection should be ruled out. The earlier a late infection is caught, the more treatment options are available and the better the odds of keeping your implant.

Implant Coatings and Future Prevention

One of the more promising areas of research focuses on making the implant surfaces themselves resistant to bacterial colonization in the first place. Several technologies are under development or in early clinical use. Silver coatings have been adopted in prosthetic oncology (implants used after tumor removal) with favorable results, and researchers are now exploring silver combined with hydroxyapatite for standard joint replacements. Antibiotic-loaded hydrogel coatings, which slowly release antimicrobial agents over time, are another approach. Iodine coatings have also shown protective effects against prosthetic joint infections in early studies.¹⁹ Separately, researchers are exploring nanoscale surface modifications on titanium that physically disrupt bacterial attachment, creating a surface topography that makes it harder for biofilms to form.³

None of these technologies has yet become the standard of care for routine knee replacements, and it will likely take years of clinical data before any of them are widely adopted. But the direction of the field is clear: the goal is to design implants that actively resist infection rather than relying solely on a patient’s immune system and surgical technique to keep bacteria away. For anyone living with a knee replacement today, the best strategy remains the basics: managing your overall health, treating other infections promptly, and speaking up when something does not feel right in your knee.