Knee Replacement: Understanding Periprosthetic Joint Infection (PJI), Symptoms, and Treatment

What is the most common infection after knee replacement?

The most common and significant infection following knee replacement surgery (total knee arthroplasty) is a Periprosthetic Joint Infection (PJI), which occurs when bacteria colonize the artificial joint and surrounding tissues. This serious complication can significantly impede recovery and necessitate further medical or surgical intervention.

The Primary Concern: Periprosthetic Joint Infection (PJI)

Periprosthetic Joint Infection (PJI) is the most devastating complication after total knee arthroplasty (TKA). It involves the presence of microorganisms, typically bacteria, within the joint space and on the surfaces of the prosthetic components. This infection can lead to persistent pain, swelling, stiffness, and in severe cases, necessitate revision surgery or even amputation. While the overall incidence of PJI is relatively low (ranging from 0.5% to 2% in primary TKA), its impact on patient morbidity, healthcare costs, and long-term outcomes is substantial.

How Infections Occur

Bacteria can enter the surgical site through several pathways, leading to PJI. Understanding these routes is crucial for prevention:

• Intra-operative Contamination: This is the most common route. Bacteria, often from the patient's own skin (e.g., Staphylococcus aureus or coagulase-negative staphylococci like Staphylococcus epidermidis), or less commonly from the surgical environment, can directly contaminate the wound during the operation.
• Hematogenous Spread: Bacteria from a distant site of infection in the body (e.g., a urinary tract infection, dental abscess, skin infection) can travel through the bloodstream and seed the artificial joint. This can occur weeks, months, or even years after the initial surgery.
• Wound Complications: Poor wound healing, persistent drainage, or a superficial surgical site infection can create an entry point for bacteria, leading to a deeper PJI.

Infections are often categorized by their timing relative to the surgery:

• Early-Onset Infections: Occur within the first few weeks to three months post-surgery, often due to intra-operative contamination. These typically present with acute pain, swelling, and systemic signs of infection.
• Delayed-Onset Infections: Manifest between 3 months and 2 years after surgery. These can be more insidious, potentially stemming from less virulent organisms or subtle wound issues.
• Late-Onset Infections: Appear more than 2 years post-surgery, almost always due to hematogenous spread from a distant source of infection.

Recognizing the Signs and Symptoms

Early detection of PJI is paramount for successful treatment and preserving joint function. Be vigilant for the following signs:

• Persistent or Worsening Pain: While some post-operative pain is expected, pain that is increasing, unremitting, or disproportionate to activity level, especially after the initial recovery period, is a red flag.
• Swelling and Redness: Continued or new onset of significant swelling and redness around the knee, beyond the expected post-surgical inflammation.
• Warmth: The skin around the knee joint feeling abnormally warm to the touch.
• Fever or Chills: Systemic signs of infection, indicating the body's immune response.
• Pus Drainage: Any leakage of pus or cloudy fluid from the surgical incision.
• Stiffness or Restricted Movement: A sudden or progressive loss of range of motion in the knee, often accompanied by pain.
• Fatigue and Malaise: General feelings of unwellness or low energy.

It is crucial to contact your orthopedic surgeon immediately if you experience any of these symptoms. Delay in diagnosis and treatment significantly worsens the prognosis.

Diagnosis of PJI

Diagnosing PJI requires a comprehensive approach, combining clinical assessment with laboratory and imaging studies:

• Clinical Examination: The surgeon will assess the knee for warmth, swelling, redness, pain, and any signs of wound breakdown or drainage.
• Blood Tests:
  • Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP): These inflammatory markers are typically elevated in the presence of infection. While useful, they can also be elevated due to other post-surgical inflammation.
  • Complete Blood Count (CBC): May show an elevated white blood cell count.
• Joint Fluid Aspiration and Analysis (Arthrocentesis): This is the gold standard for diagnosis. Fluid is drawn from the knee joint and analyzed for:
  • White Blood Cell (WBC) Count and Differential: Elevated cell counts, particularly neutrophils, are highly indicative of infection.
  • Culture: The fluid is cultured to identify the specific bacteria causing the infection, which guides antibiotic selection.
• Imaging Studies:
  • X-rays: May show signs of loosening of the prosthetic components, bone destruction, or periosteal reaction, though these are often late signs.
  • Bone Scans or PET Scans: Can help identify areas of increased metabolic activity consistent with infection, but are not always specific.

Treatment Approaches

Treatment for PJI is complex and typically involves a combination of long-term antibiotic therapy and surgical intervention. The specific approach depends on the timing of the infection, the type of bacteria, and the patient's overall health.

• Antibiotic Therapy:
  • Intravenous (IV) Antibiotics: Often initiated immediately after diagnosis, targeting the most likely organisms.
  • Oral Antibiotics: Follow IV therapy, usually for an extended period (weeks to months), once the specific pathogen is identified and its antibiotic sensitivities are known.
• Surgical Intervention:
  • Debridement and Retention of Prosthesis (DAIR): For early, acute infections with a stable prosthesis, the joint is surgically cleaned, infected tissues are removed, and the prosthesis is thoroughly washed, followed by prolonged antibiotic therapy.
  • One-Stage Exchange Arthroplasty: The infected prosthesis is removed, the joint is thoroughly cleaned, and a new prosthesis is implanted in the same surgical setting. This is typically reserved for select cases with certain types of bacteria and good bone stock.
  • Two-Stage Exchange Arthroplasty: This is the most common and often most successful surgical approach for established PJI.
    1. First Stage: The infected prosthesis is removed, the joint is thoroughly debrided, and an antibiotic-impregnated cement spacer is temporarily implanted. The patient then receives a prolonged course of IV antibiotics (usually 6-8 weeks).
    2. Second Stage: Once the infection markers normalize and the patient is deemed infection-free, the spacer is removed, and a new knee prosthesis is implanted.
  • Arthrodesis (Fusion): In severe, intractable cases, fusing the knee joint may be considered to eliminate the infection, though it results in a stiff, non-moving knee.
  • Amputation: In rare, life-threatening cases where other treatments have failed and the infection is uncontrolled, amputation may be necessary.

Minimizing Your Risk

While no measure can guarantee complete prevention, several strategies can significantly reduce the risk of PJI:

• Pre-operative Optimization:
  • Dental Health: Address any dental infections before surgery.
  • Skin Health: Treat any skin infections (e.g., rashes, open sores) prior to surgery.
  • Urinary Tract Infections (UTIs): Ensure any UTIs are cleared before surgery.
  • Diabetes Control: Patients with diabetes should have their blood sugar levels well-controlled.
  • Smoking Cessation: Quitting smoking significantly improves wound healing and reduces infection risk.
  • Weight Management: Achieving a healthy weight can reduce surgical complications.
  • Pre-operative Antibiotics: You will receive antibiotics shortly before surgery to reduce bacterial load.
• Intra-operative Measures: Surgeons and surgical teams adhere to strict sterile protocols, including specialized air filtration, operating room cleanliness, and meticulous surgical technique.
• Post-operative Care:
  • Wound Care: Follow all instructions for incision care, keeping it clean and dry.
  • Antibiotics: Complete any prescribed post-operative antibiotic courses.
  • Avoid Infection Sources: Be vigilant about treating any new infections promptly. Inform medical professionals about your knee replacement when seeking treatment for any infection.
  • Prophylactic Antibiotics: Your surgeon may recommend prophylactic antibiotics for certain procedures (e.g., dental work, invasive medical procedures) for a period after your surgery, especially if you have risk factors.
• Long-Term Vigilance: Remain aware of the signs and symptoms of infection throughout your life.

The Importance of Early Intervention

Periprosthetic Joint Infection is a serious complication that can severely compromise the success of knee replacement surgery and significantly impair a patient's mobility and quality of life. As an Expert Fitness Educator, I emphasize that the ability to engage in rehabilitation, regain strength, and return to desired activities hinges on a healthy, infection-free joint. Prompt recognition of symptoms and immediate medical attention are critical for achieving the best possible outcome and preserving the function of your new knee.

Conclusion

While knee replacement surgery is highly successful for restoring mobility and alleviating pain, the risk of Periprosthetic Joint Infection (PJI) remains a significant concern. By understanding the nature of PJI, recognizing its symptoms, and adhering to preventative measures, patients can play an active role in safeguarding their surgical outcome and ensuring the long-term health and function of their new knee.