Knee Replacement Infection: Treatment, Risks, and Prevention

A knee replacement is supposed to be your “new knee, who dis?” momentless pain, more walking, fewer
dramatic sighs when you stand up. But on rare occasions, bacteria crash the party and turn a smooth recovery
into a high-stakes game of “Is that normal swelling… or something else?”

This guide explains what knee replacement infections (often called periprosthetic joint infections, or PJI)
look like, why they happen, how doctors diagnose and treat them, and what you can do to lower your risk.
It’s in-depth, practical, and yeslightly humorousbecause fear does not deserve the last word.
(Also: no, you cannot “power through” a serious infection with vibes and vitamin gummies.)

What counts as a knee replacement infection?

A knee replacement infection happens when germs (usually bacteria) grow in the tissues around the artificial
joint. Infections can be:

• Superficial (incisional): mostly skin and tissue near the incision.
• Deep (joint/prosthesis-related): involves the space around the implant and is more serious.

Deep infections are especially tricky because bacteria can form a sticky “biofilm” on metal and plastic
surfaces. Biofilm is like a microscopic raincoat: it helps bacteria hide from your immune system and makes
antibiotics less effective unless you also remove infected tissueand sometimes the implant itself.

How common is it?

Knee replacement infection is uncommon, but not “mythical unicorn” uncommon. Published estimates vary
based on patient health, hospital factors, and follow-up time. A large guideline summary cites about
~1.55% within two years after knee replacement in the referenced literature.
The risk is generally higher after revision surgery (a second or third operation on the same knee).

The takeaway: the odds are in your favor, but the consequences are serious enough that early recognition and
prevention matter a lot.

When can an infection happen?

Infections are often described by timing:

• Early: within days to weeks after surgery (often linked to the surgical wound).
• Delayed: weeks to months after surgery (sometimes subtlepain may be the main clue).
• Late: months to years later (can occur if bacteria travel through the bloodstream from another
  infection elsewhere in the body).

Late infections sound unfair (because they are). But they’re a reminder that a replacement joint is not a
sealed fortressbloodborne bacteria can still visit.

Risk factors: why some people are more vulnerable

Think of infection risk as a “stacking” problem. One risk factor might not change much; several together can.
Risk factors often fall into three buckets:

1) Patient/health factors

• Diabetes (especially if blood sugar is not well controlled)
• Obesity (higher surgical complexity and wound-healing challenges)
• Immune suppression (e.g., chemotherapy, chronic steroid use, certain autoimmune medications)
• Poor circulation (peripheral vascular disease)
• Inflammatory arthritis (and/or medications used to treat it)
• Smoking (affects blood flow and healing)
• Malnutrition or anemia (less common to talk about, but not rare in real life)

2) Surgical and hospital factors

• Longer operating time and higher complexity
• More operating-room traffic (more door openings = more airborne particles)
• Revision surgery (already-operated tissue is less forgiving)

3) “Bacteria opportunity” factors

• Skin breaks or wounds (even small ones)
• Active skin infections
• Infections elsewhere in the body that can spread through blood (e.g., urinary infections, dental abscesses, skin infections)

Notably, many risks are modifiable. That’s good news because “modifiable” is another way of saying
“something you and your care team can actually do something about.”

Signs and symptoms: what should raise suspicion?

Some symptoms overlap with normal surgical recoveryespecially in the first couple weeksso context matters.
That said, the classic warning signs include:

• Increasing pain or stiffness after you were previously improving
• Swelling that worsens rather than slowly settles
• Warmth and redness around the incision or knee
• Drainage (blood, cloudy fluid, pus, or persistent leaking)
• Fever, chills, night sweats
• Fatigue that feels out of proportion

A special note on pain: it’s common after knee replacement, but infection pain often has a
“wrong direction” patternworse day to day instead of gradually better. Late infections can also show up
as pain and swelling months or years later, sometimes with a feeling that the joint is loosening or unstable.

If you have rapidly worsening pain, spreading redness, significant drainage, confusion, shortness of breath,
or high fever, treat it as urgent. Your knee is important; your bloodstream is even more so.

How doctors diagnose a suspected infection

Diagnosing PJI is part detective work, part lab science, and part “please hold still while we examine your knee.”
A typical evaluation includes:

Medical history + exam

Your surgeon (or urgent care team) will ask about symptom timing, wound healing, recent infections elsewhere,
and any antibiotics you’ve taken recently (important because antibiotics can make cultures harder to interpret).

Blood tests (screening, not a final verdict)

Two common testsCRP (C-reactive protein) and ESR (erythrocyte sedimentation rate)measure inflammation.
They don’t “prove” infection by themselves, but normal results make infection less likely, and elevated results
raise suspicion (especially beyond the immediate post-op window).

Joint aspiration (a key step)

If infection is a serious possibility, doctors often remove a small amount of joint fluid with a needle
(aspiration). That fluid can be tested for:

• White blood cell count and neutrophil percentage
• Bacterial cultures (aerobic and anaerobic)
• Leukocyte esterase (a quick inflammatory marker)
• Alpha-defensin (a biomarker used in many centers)
• Other tests depending on the case and lab availability

Imaging

X-rays can help evaluate loosening or bone changes. Other imaging (like nuclear medicine scans) may be used
in selected cases, but imaging alone often can’t reliably “confirm” infection. It’s usually interpreted alongside
labs and aspiration results.

Treatment options: what happens if infection is confirmed?

Treatment depends on timing (early vs late), the bacteria involved, implant stability, tissue condition,
and your overall health. The goal is to eradicate infection while preserving the best knee function possible.

1) Antibiotics alone (limited situations)

If the problem is superficial and truly limited to skin/soft tissue, antibiotics (and close monitoring) may be enough.
But if the infection involves the joint space or implant, antibiotics alone usually aren’t sufficient because of biofilm.

2) DAIR: Debridement, antibiotics, and implant retention

For some early infections, surgeons may recommend debridementcleaning out infected tissue,
washing the joint, and often replacing modular plastic parts (like the liner) while keeping the metal components.
This approach is commonly paired with a prolonged antibiotic course (often weeks), guided by an infectious
disease specialist.

DAIR can be appealing because it may preserve the implant and shorten the “rebuild the knee” journeybut
success depends heavily on timing, organism type, and implant stability.

3) One-stage exchange (select cases)

In a one-stage exchange, surgeons remove the implant, clean the area thoroughly, and place a new implant
in the same operation. This approach is used in carefully selected situations, often when the organism is known,
soft tissue is in good shape, and the surgical team has strong experience with the method.

4) Two-stage revision (common for late or established infections)

Two-stage revision is often used for late infections or infections that have been present longer.
It usually works like this:

1. Stage 1: Remove the implant, wash out infected tissue, and place an antibiotic spacer.
2. Antibiotic phase: Receive IV (and sometimes oral) antibiotics for a prolonged periodoften around 6 weeks or longer, depending on the case.
3. Stage 2: Once infection control is confirmed, remove the spacer and implant a new knee replacement.

Spacers help maintain joint space and can improve comfort and mobility compared with leaving the knee “empty.”
They’re typically made with antibiotic-loaded cement that releases medication locally over time.

5) Long-term suppressive antibiotics (when surgery isn’t an option)

Sometimes a patient can’t safely undergo major surgery (or chooses not to). In those cases, doctors may use
long-term antibiotic suppression to control symptoms and limit bacterial growth. It may not “cure” the infection,
but it can be a practical strategy when risks of surgery outweigh benefits.

6) Salvage procedures (rare, but real)

If infection is severe and repeated attempts fail, options like knee fusion (arthrodesis) or, very rarely,
amputation may be discussed. These are last-resort scenarios, but they’re part of honest informed consent:
infections can be life-altering, and treatment sometimes requires tough trade-offs.

What are the risks if infection isn’t treated quickly?

Untreated or delayed treatment can lead to implant loosening, bone loss, stiffness, repeated surgeries, and
prolonged disability. It can also become a systemic infection (sepsis), which is a medical emergency.
Beyond the physical risks, many patients describe infection as emotionally exhaustinglike recovering from
surgery while also negotiating with uncertainty.

Prevention: what hospitals and surgeons do (and why it works)

Infection prevention is multi-layered. No single step is magical; the power is in stacking several evidence-based
practices together.

Before surgery

• Pre-op bathing/showering the night before (or per your facility’s protocol)
• Screening and decolonization in some centers (for example, nasal testing and targeted ointment if needed)
• Optimizing blood sugar and treating active infections elsewhere (skin, urinary, dental, etc.)

During surgery

• Prophylactic antibiotics timed so effective levels are present when the incision is made
• Alcohol-based skin prep unless contraindicated
• Strict sterile technique, instrument sterilization, and minimizing operating-room traffic
• Glycemic control (even for patients without diabetes) and maintaining normal body temperature

After surgery

• Appropriate incision care and follow-up
• Avoiding unnecessary antibiotic “extras” unless there’s a specific indication
• Early evaluation of drainage or wound healing problems

Prevention: what you can do (the patient checklist that actually matters)

Here’s the practical partwhat patients can do that moves the needle:

1) Get your “modifiable risks” in shape

• Blood sugar: aim for well-controlled diabetes before surgery (ask what target your team wants)
• Smoking: quitting is one of the most powerful steps for wound healing
• Weight: even modest loss can reduce wound complications in some patients
• Nutrition: ask if you should be screened for anemia or low protein if you’ve had recent weight loss or poor appetite

2) Protect your skin like it’s the VIP entrance

Any cuts, rashes, insect bites, or infected hangnails on the surgical leg are worth telling your surgeon about.
The goal is to avoid bringing bacteria to surgery on a “technicality.” (Bacteria love technicalities.)

3) Follow pre-op cleaning instructions exactly

If you’re given chlorhexidine (CHG) wipes or a wash protocol, use it as directed. Don’t improvise with
“extra scrubbing” that irritates skinirritated skin is not a win.

4) Be smart about dental work and other procedures

Some surgeons recommend antibiotics before certain dental procedures for select patients, but many people
do not need routine pre-dental antibiotics, and evidence for prevention is limited. The important action:
tell your dentist you have a joint replacement and follow the shared plan between your dentist and surgeon.

When to call your surgeon (or seek urgent care)

Contact your care team promptly if you have:

• New or worsening drainage from the incision
• Redness that spreads, warmth that increases, or swelling that escalates quickly
• Fever with knee pain, chills, or night sweats
• Sudden increase in pain after a period of improvement
• Symptoms months or years later that include new swelling, pain, or instability

If you feel seriously ill (confusion, very high fever, rapid heart rate, trouble breathing), seek emergency care.
This is not “wait and see” territory.

Final takeaway

Knee replacement infections are uncommon, but they’re one of the most important complications to recognize early.
The best outcomes come from fast evaluation, proper testing (often including aspiration), and a treatment plan that
matches the timing and severitywhether that’s DAIR, staged revision, targeted antibiotics, or carefully chosen alternatives.
Prevention is real and effective, especially when patient optimization and surgical best practices work together.

Experiences: what recovery and treatment can feel like in real life (about )

People rarely expect the emotional curveball of a suspected infection. Many patients describe a specific moment:
the day they notice the knee is getting worse instead of bettermore swelling, more heat, more pain, or drainage
that just won’t quit. The first reaction is often denial (“It’s probably normal”), closely followed by bargaining
(“I’ll rest one more day”), and then a late-night spiral of internet searches. If that’s you: you’re not dramatic;
you’re attentive. In this scenario, attention is a superpower.

The diagnostic process can also feel intense. Blood tests are easy enough, but joint aspiration is the step that
makes people nervous. Patients often report it’s less painful than they feareduncomfortable, yes, but quick
and the reassurance of getting real data can be worth a lot. There’s also a strange psychological shift when a
doctor starts using words like “cultures,” “cell count,” and “organism.” It turns your knee from a body part into
a science project. Not your favorite genre, but it’s how the right treatment gets chosen.

If treatment involves surgery, the logistics become part of life. People who go through DAIR often talk about
hoping it’s the “one and done” fixclean it out, swap the plastic liner, take antibiotics, move on. When it works,
patients feel like they dodged a major detour. When it doesn’t, the disappointment is real, and it’s important to
know that “needing more treatment” isn’t a personal failureit’s biology and timing and biofilm being stubborn.

Two-stage revision is a bigger chapter. Many patients say the spacer phase is the oddest: you’re in-between.
You may have mobility limitations, physical therapy that looks different, and a calendar that suddenly includes
IV antibiotics. Some patients get a PICC line and learn a whole new routineflushes, dressing changes, timing
doses around sleep and meals. It can feel like your home becomes a mini-clinic. The upside is that many people
also describe a surprising sense of teamwork: orthopedics, infectious disease, nursing, and family all pulling in
the same direction. If you’re doing this, it’s okay to ask for help and to treat “organization” as a medical tool.
(Label makers are not just for craft rooms. They are for survival.)

On the prevention side, patients often say they wished they’d taken pre-op optimization more seriouslynot out
of guilt, but out of clarity. Quitting smoking earlier, getting blood sugar tighter, reporting that “tiny” rash,
or rescheduling surgery until a skin issue healed can feel annoying in the moment. But many people later view
it as protecting their future self. And perhaps the most common experience of all: relief when a worried call to
the surgeon ends with a clear plan. Even when the plan is hard, uncertainty is often harder.

If you’re reading this because you’re anxious, remember: most knee replacements do well. And when infections
do happen, modern diagnosis and treatment strategies exist for a reasonbecause people get through this.
Ask questions, keep records of symptoms, follow your care team’s instructions, and don’t let embarrassment
delay an important evaluation. Your job is not to be “tough.” Your job is to be safe.