Knee Replacement Infection Protocol (Periprosthetic Joint Infection - PJI)
This protocol outlines the evaluation and management of infection following total knee arthroplasty (TKA). Treatment depends on the timing, severity, and organism involved.
1. Classification of Infection Timing
| Type |
Time after surgery |
Typical cause |
Approach |
| Early infection |
Within 4 weeks |
Operative contamination |
Debridement and implant retention (DAIR) |
| Delayed infection |
1–12 months |
Low-virulence organisms (e.g., Coagulase-negative Staph) |
Consider staged exchange |
| Late infection |
After 1 year |
Hematogenous spread |
Often requires implant removal |
2. Diagnostic Protocol
Clinical Signs
- Pain, swelling, redness, warmth around the knee
- Persistent wound drainage
- Fever (sometimes absent)
Laboratory Tests
- ESR and CRP: Elevated values suggest infection (CRP >10 mg/L, ESR >30 mm/hr)
- CBC: WBC may be normal or mildly raised
- Joint aspiration: >3,000 cells/µL and >65% neutrophils indicate infection; send for culture
- Alpha-defensin test: Highly specific and sensitive
- Intraoperative cultures: At least 3 samples should be collected
Imaging
- X-ray: Loosening, periosteal reaction, osteolysis
- Bone or WBC scan: Used if diagnosis uncertain
3. Treatment Protocol
A. Early Infection (within 4 weeks)
Goal: Save the implant if possible.
- Procedure: Debridement, Antibiotics, and Implant Retention (DAIR)
- Exchange of modular parts (polyethylene liner)
- Empirical IV antibiotics until culture report is available
- Culture-specific antibiotics for 6 weeks IV + 6–12 weeks oral
B. Chronic Infection (more than 4 weeks)
1. Two-Stage Revision (Gold Standard)
- Stage 1: Remove implants, debridement, insert antibiotic cement spacer, IV antibiotics for 6 weeks
- Stage 2: Re-implant new prosthesis after CRP/ESR normalize and cultures are negative
2. One-Stage Revision
- For known organism, good soft tissue, sensitive bacteria
- Implant removed and replaced in the same surgery
- IV antibiotics for 6 weeks
C. Suppressive Antibiotic Therapy
- Used in patients unfit for surgery (elderly, comorbidities)
- Long-term or lifelong oral antibiotics (e.g., doxycycline, TMP-SMX)
- Goal: Control infection, relieve symptoms
D. Salvage Options
- Knee arthrodesis (fusion)
- Amputation (last resort)
4. Common Organisms
| Organism |
Notes |
| Staphylococcus aureus (MSSA/MRSA) |
Most common |
| Coagulase-negative Staphylococci |
Common in chronic infections |
| Streptococcus, Enterococcus |
Less common |
| Gram-negative bacilli (Pseudomonas, E. coli) |
Hospital-acquired infections |
| Cutibacterium acnes |
Low-grade, delayed infections |
5. Typical Antibiotic Regimens (Example)
| Organism |
IV phase (6 weeks) |
Oral phase (6–12 weeks) |
| MSSA |
Cefazolin or Nafcillin |
Dicloxacillin or Cephalexin |
| MRSA |
Vancomycin or Daptomycin |
Linezolid or TMP-SMX |
| CoNS |
Vancomycin |
Rifampicin + Doxycycline |
| Gram-negative |
Piperacillin-tazobactam or Cefepime |
Ciprofloxacin |
