What is the recommended treatment for an older adult with a history of orthopedic surgery who has a prosthetic knee infection?

Treatment of Prosthetic Knee Infection in Older Adults

Prosthetic knee infection requires combined surgical and antimicrobial management, with the surgical approach (debridement with retention vs. prosthesis exchange) determined by infection timing and clinical factors, followed by 4-6 weeks of pathogen-specific intravenous antibiotics. 1

Multidisciplinary Approach Required

• Strong collaboration between orthopedic surgeons, infectious disease specialists, and general internists is essential for optimal outcomes and to reduce morbidity and mortality. 1
• Shared decision-making with the patient is critical, particularly when treatment goals of infection eradication and joint function preservation may conflict. 1

Diagnostic Workup Before Treatment

Obtain Cultures Before Starting Antibiotics

• Collect at least 3-6 periprosthetic tissue samples from different sites during surgery for aerobic and anaerobic cultures. 2, 3
• If arthrocentesis is performed preoperatively, withhold antimicrobials for at least 2 weeks prior if the patient is medically stable. 2
• Avoid superficial wound swabs as they are misleading and promote unnecessarily broad antimicrobial treatment. 1

Surgical Management Strategy

Acute Infection (< 3 weeks from surgery or < 3 weeks of symptoms with hematogenous spread)

• Debridement and implant retention (DAIR) with exchange of polyethylene insert is the preferred approach. 1, 4
• This involves arthrotomy, thorough debridement, and exchange of removable components while retaining the fixed prosthesis. 1

Chronic Infection (> 3 weeks duration)

• Two-stage exchange arthroplasty is the standard approach for chronic prosthetic knee infections. 1, 4
• First stage: Remove infected prosthesis and cement, insert antimicrobial-impregnated cement spacer. 1
• Second stage: Reimplant new prosthesis after 6 weeks (or 2-4 weeks for early exchange). 1
• Be aware that 52% of patients experience complications during two-stage treatment, with 18% mortality at mean 3.7 years follow-up. 5

Salvage Options for Treatment Failure

• Prosthesis resection with or without arthrodesis, or amputation are reserved for recalcitrant infections when joint function cannot be preserved. 1

Antimicrobial Therapy

Duration Based on Surgical Strategy

For DAIR (Debridement and Implant Retention):

• 4-6 weeks of pathogen-specific IV or highly bioavailable oral therapy following debridement. 1
• For staphylococcal infections with retained prosthesis: 6 months total duration for knee infections (3 months for hip). 3

For Prosthesis Exchange:

• 4-6 weeks of pathogen-specific therapy starting after prosthesis removal. 1, 3

Pathogen-Specific Regimens

Methicillin-Susceptible Staphylococci:

• Preferred: Nafcillin 1.5-2g IV q4-6h, Cefazolin 1-2g IV q8h, or Ceftriaxone 1-2g IV q24h. 3
• Alternative: Vancomycin 15 mg/kg IV q12h (only for allergies). 1

Methicillin-Resistant Staphylococci:

• Preferred: Vancomycin 15 mg/kg IV q12h. 3

Beta-Hemolytic Streptococci (including Group B Strep):

• Preferred: Penicillin G 20-24 million units/day IV or Ceftriaxone 1-2g IV q24h. 6
• Alternative: Cefazolin 1-2g IV q8h for non-anaphylactic penicillin allergy. 6

Enterococci (Penicillin-Susceptible):

• Preferred: Penicillin G 20-24 million units IV q24h continuously or Ampicillin 12g IV q24h continuously. 3

Pseudomonas aeruginosa:

• Preferred: Cefepime 2g IV q12h or Meropenem 1g IV q8h. 3

Chronic Oral Suppression (When Prosthesis Retained)

Methicillin-Susceptible Staphylococci:

• Cephalexin 500 mg PO tid or qid, or Dicloxacillin 500 mg PO tid or qid. 1, 3

Methicillin-Resistant Staphylococci:

• Cotrimoxazole 1 DS tab PO bid, or Minocycline/Doxycycline 100 mg PO bid. 1, 3

Streptococci:

• Penicillin V 500 mg PO bid to qid, or Amoxicillin 500 mg PO tid. 1, 6

Critical Monitoring and Safety Considerations

• Adjust all antimicrobial dosages based on renal and hepatic function. 1
• Monitor for QTc prolongation and tendinopathy when using fluoroquinolones. 1
• Discuss and monitor for Clostridium difficile colitis with any antimicrobial. 1
• Never use rifampin as monotherapy due to rapid resistance development. 3
• Follow published IDSA guidelines for monitoring outpatient IV antimicrobial therapy. 1, 3

Common Pitfalls to Avoid

• Do not start antibiotics before obtaining adequate cultures unless the patient is septic or hemodynamically unstable. 2, 3
• Do not rely on superficial wound swabs for microbiologic diagnosis—they are misleading. 1
• Do not use rifampin for streptococcal infections—it is only indicated for staphylococcal PJI. 6
• Recognize that treatment failure occurs in over 20% of cases, requiring reassessment of surgical and antimicrobial strategies. 1
• Consider atypical organisms (including mycobacteria) in infections not responding to traditional management. 7

Treatment Failure Management

• If infection persists despite initial treatment, reassess surgical adequacy (biofilm removal, debridement quality). 1
• Consider more aggressive surgical intervention including two-stage exchange if DAIR fails, or prosthesis resection for recalcitrant cases. 1
• Reevaluate microbiologic diagnosis—consider sonication of explanted prosthesis and extended culture techniques for fastidious organisms. 1, 2
• Involve infectious disease consultation early for complex or culture-negative cases. 2