What is the treatment for a post-operative infection in the knee after a total knee arthroplasty (TKA) that occurred a few weeks ago?

Treatment of Post-TKA Infection at a Few Weeks Post-Surgery

For a knee infection occurring a few weeks after TKA, immediate diagnostic workup with ESR, CRP, and joint aspiration is mandatory, followed by surgical debridement with prosthesis retention if diagnosed within 3-4 weeks of symptom onset, though success rates are limited and two-stage revision remains the definitive treatment for most cases. 1, 2

Immediate Diagnostic Workup

Obtain ESR, CRP, and serum interleukin-6 immediately to evaluate for periprosthetic joint infection before initiating any treatment. 1 CRP demonstrates 73-91% sensitivity and 81-86% specificity for prosthetic knee infection when using a cutoff of 13.5 mg/L. 3 The combination of ESR and CRP achieves 93% sensitivity, 100% specificity, and 97% accuracy when at least 2 of 3 tests are abnormal. 3

Critical Pre-Aspiration Considerations

• Withhold antibiotics for at least 2 weeks prior to joint aspiration if clinically feasible (with careful monitoring for sepsis), as preaspiration antibiotic treatment causes false-negative aspirations. 4
• As long as a month off antibiotics may be necessary for cultures to become positive. 4
• Do not rely on peripheral WBC counts—they are not elevated in most patients with infected prostheses, making normal WBC meaningless for excluding infection. 1, 3

Joint Aspiration Protocol

Proceed immediately with image-guided knee joint aspiration (fluoroscopy or ultrasound) for synovial fluid analysis when inflammatory markers are elevated or clinical suspicion is high. 4, 1

• Synovial fluid should be evaluated with total and differential cell counts, aerobic and anaerobic bacterial cultures, leukocyte esterase, alpha-defensin, CRP, and nucleic acid amplification testing. 4
• Synovial fluid WBC counts >1,700 cells/µL and differential >69% polymorphonuclear cells indicate high suspicion for infection. 2
• A "dry tap" does not exclude infection—weekly repeat aspirations are recommended if initial aspiration is negative and clinical suspicion remains high. 4
• If preoperative cultures are positive, intraoperative synovial fluid re-cultures are still necessary, and any discordance should be noted. 4

Obtain Baseline Radiographs

Get knee radiographs as initial imaging to look for signs of loosening, osteolysis, or component migration that may accompany infection. 1, 3

Treatment Algorithm Based on Timing

Acute Infection (Within 3-4 Weeks of Symptom Onset)

Irrigation, debridement, and prosthesis retention can be attempted for acute infections with symptom duration less than 3-4 weeks, though success rates are limited, particularly with staphylococcal species. 5, 2

• The duration of symptoms prior to operation critically affects outcome—patients must be treated as soon as possible. 5
• Success rates for prosthesis retention are significantly lower with staphylococcal infections (0% survival in one series) compared to non-staphylococcal species (100% survival). 5
• Staphylococcus aureus and coagulase-negative Staphylococcus species are the most common organisms. 4, 3

Surgical technique for debridement:

• Perform open debridement with thorough irrigation. 5, 6
• Consider using vacuum constriction devices to improve irrigation efficiency. 5
• Inject the most sensitive antibiotics (based on culture) into irrigation saline. 5
• Polyethylene liner exchange should be performed during debridement. 6

Chronic Infection (Beyond 3-4 Weeks)

Two-stage revision arthroplasty is the gold standard for infections beyond the acute window and remains the most effective method to control chronic infection and restore knee function. 7, 6, 2

First Stage: Explantation and Spacer Placement

• Remove all prosthetic components and cement. 6
• Perform thorough debridement of infected tissue. 6
• Place antibiotic-impregnated bone cement spacer (static or dynamic). 7, 6
• Adding 4g of teicoplanin to the cement shortens the time between stages and duration of antibiotic therapy. 7

Interval Between Stages

• Reimplantation within 10 weeks after first stage is associated with better range of motion outcomes. 7
• No significant difference in Knee Society Scores was found comparing intervals shorter or longer than 10 weeks. 7
• Use of dynamic spacers is associated with better ROM outcomes compared to static spacers. 7
• Monitor CRP and ESR levels—these are safe parameters for determining reimplantation timing. 7

Second Stage: Reimplantation

• Obtain intraoperative tissue cultures from multiple sites for aerobic and anaerobic bacterial culture, even if preoperative aspiration was positive. 4
• Perform intraoperative frozen section analysis of periprosthetic synovial tissue. 4

Antibiotic Therapy

Cefazolin is FDA-approved for perioperative prophylaxis in prosthetic arthroplasty and may be continued for 3-5 days following surgery when infection risk is particularly devastating. 8 However, definitive antibiotic selection for established infection must be based on culture and sensitivity results targeting the specific organism identified. 8, 5

Critical Pitfalls to Avoid

• Do not rely on absence of fever, erythema, or warmth to exclude infection—chronic infections frequently present with pain alone. 1, 3
• Night pain or pain at rest characteristically indicates infection, whereas pain on weight-bearing suggests mechanical loosening. 4, 3
• Open debridement with liner change has low success rates for acute methicillin-resistant Staphylococcus aureus infections. 6
• Two-stage revision carries a potential risk of re-infection (10.4% in one series at mean 48.8-month follow-up). 7
• Arthroscopic debridement may be considered for acute hematogenous infections but has limited success for other infection types. 6