What is the treatment for an infection of a partial knee replacement?

Treatment of Partial Knee Replacement Infection

The optimal treatment for an infected partial knee replacement is a two-stage revision with complete removal of all prosthetic components, thorough debridement of infected tissue, placement of an antibiotic-loaded cement spacer, followed by prolonged targeted antimicrobial therapy (minimum 6 weeks) and delayed reimplantation after confirmed infection eradication. 1

Surgical Management Algorithm

Two-Stage Revision (Preferred Approach)

Complete removal of all components and infected material is essential for treatment success. 1

• First stage: Remove all prosthetic components, infected cement, and perform complete excision of infected bone and soft tissues 1
• Place an antibiotic-loaded cement spacer (articulating preferred for maintaining soft tissue envelope and patient mobility) 2, 3
• Collect minimum of three intraoperative tissue specimens for culture, including specific mycobacterial cultures if initial cultures are negative 1
• Delayed reimplantation timing: Minimum 6 weeks after first stage, with some protocols recommending up to 6 months for difficult infections 1
• Critical before reimplantation: Confirm infection eradication through multiple preoperative joint aspirations and normalized inflammatory markers (ESR and CRP) 1

Single-Stage Revision (Limited Indications)

Single-stage revision may be considered only when ALL of the following criteria are met 1, 4:

• Pathogen identity known preoperatively with documented susceptibility to oral antibiotics with excellent bioavailability
• Good soft tissue envelope present
• No bone grafting required
• Patient medically unable to tolerate multiple surgeries

However, infection recurrence is significantly higher with single-stage procedures due to mature biofilm formation, making this approach not recommended over two-stage revision. 1

Debridement, Antibiotics, and Implant Retention (DAIR)

DAIR has high failure rates and should be avoided except in very early acute infections (symptoms <3 weeks, prosthesis in place <3 months) 5. Key factors predicting DAIR failure include:

• Presence of sinus tract 5
• Immunocompromised patient 5
• Staphylococcal infection, particularly MRSA 5
• Delay between symptom onset and debridement 5

Antimicrobial Therapy

Duration and Regimen

Total knee arthroplasty infections require 6 months of antimicrobial therapy following two-stage revision. 1

• Initial phase: 2-6 weeks of pathogen-specific intravenous antimicrobial therapy 1
• Continuation phase: Oral antimicrobials to complete total 6-month course 1

Staphylococcal Infections (Most Common)

For staphylococcal PJI, rifampin-based combination therapy is recommended 1:

• Rifampin 300-450 mg orally twice daily PLUS a companion drug 1
• Primary companion drugs: Ciprofloxacin or levofloxacin (fluoroquinolones preferred) 1
• Secondary companion drugs (if fluoroquinolones contraindicated): Co-trimoxazole, minocycline, doxycycline, or cephalexin 1
• Never use rifampin monotherapy due to rapid resistance development 1

Special Consideration: Nontuberculous Mycobacterial (NTM) Infections

NTM infections present indolently and can mimic aseptic loosening, with negative cultures in up to 61.5% of cases. 1

• Suspect NTM when initial cultures are negative despite clinical suspicion of infection 1
• Send multiple tissue and implant specimens specifically for mycobacterial culture 1
• Consider PCR and next-generation sequencing for culture-negative cases 1
• Require prolonged antimicrobial therapy (often >6 months) with multidrug regimens 1
• Formulate treatment plan with infectious disease specialists and pharmacists for drug-drug interaction monitoring 1

Alternative Approaches When Reimplantation Not Feasible

Permanent Resection Arthroplasty

Consider in patients with 1:

• Nonambulatory status
• Limited bone stock or poor soft tissue coverage
• Highly resistant organisms with limited treatment options
• Medical conditions precluding multiple surgeries
• Failed previous two-stage exchange with unacceptable reinfection risk

Arthrodesis

May be considered for total knee arthroplasty infections when functional benefit exists over resection arthroplasty 1

Amputation

Amputation should be the last resort but may be necessary for 1:

• Necrotizing fasciitis
• Severe bone loss preventing reconstruction
• Inability to achieve soft tissue coverage
• No available medical therapy for resistant organisms
• Prior failed resection arthroplasty or arthrodesis

Referral to a specialty center with PJI expertise is advised before proceeding with amputation except in emergent cases. 1

Critical Pitfalls to Avoid

• Never rely on superficial wound swabs - they are misleading and promote unnecessarily broad antimicrobial treatment 1
• Do not use single-stage revision as routine approach - biofilm formation makes failure rates unacceptably high 1
• Never proceed with reimplantation without confirming infection eradication - obtain multiple preoperative aspirations and normalized inflammatory markers 1
• Do not overlook NTM as causative organism - particularly in culture-negative cases with indolent presentation 1
• Avoid DAIR in chronic infections - success rates are poor except in very early acute infections 5

Multidisciplinary Approach

All prosthetic joint infections require coordination between orthopedic surgery, infectious disease specialists, and pharmacists to optimize antimicrobial regimens, monitor for adverse reactions and drug interactions, and ensure patient adherence. 1