Is a C-Reactive Protein (CRP) level greater than 200 indicative of a severe orthopedic implant infection, and can implant removal be considered as a treatment option in such cases?

CRP in Orthopedic Implant Infection and Decision for Implant Removal

A CRP greater than 200 mg/L strongly suggests severe prosthetic joint infection and warrants urgent surgical intervention, but the decision for implant removal must be based on a comprehensive diagnostic algorithm that includes clinical presentation, timing of symptoms, implant stability, and microbiological confirmation—not CRP alone.

Understanding CRP in Orthopedic Implant Infections

Diagnostic Thresholds and Performance

• CRP is elevated in orthopedic implant infections, but a level >200 mg/L is exceptionally high and indicates severe infection. The standard diagnostic cutoff for prosthetic joint infection is much lower: 13.5 mg/L for knee arthroplasty (sensitivity 73-91%, specificity 81-86%) 1, and 10.3 mg/L for hip arthroplasty 2.

• The combination of elevated ESR and CRP provides optimal diagnostic accuracy (sensitivity 93%, specificity 100%, accuracy 97%) when at least 2 of 3 inflammatory markers (CRP, ESR, fibrinogen) are abnormal 1.

• CRP must always be interpreted with ESR for suspected prosthetic joint infection, as recommended by the Infectious Diseases Society of America and American Academy of Orthopaedic Surgeons 1.

Clinical Context for CRP Interpretation

• Normal postoperative CRP peaks on day 2-3 and returns to baseline within 2 months after uncomplicated surgery 1, 3. A CRP of 200 mg/L at any point beyond the immediate postoperative period is pathological.

• A second rise in CRP after initial postoperative decline indicates a complication, with bacterial infection typically showing levels >100 mg/dl after the fourth postoperative day 3.

• Median CRP in confirmed implant infections is 51 mg/L for knee, 18 mg/L for hip, and 82 mg/L overall 2, 4, making a value of 200 mg/L highly concerning for severe infection.

Mandatory Diagnostic Workup Before Implant Removal

Required Preoperative Evaluation

You cannot proceed to implant removal based solely on CRP >200 mg/L. The following diagnostic algorithm must be completed 1:

1. Obtain blood cultures immediately if fever is present, symptoms are acute, or bacteremia is suspected (particularly with Staphylococcus aureus) 1.

2. Perform diagnostic arthrocentesis for synovial fluid analysis including:

   • Total cell count and differential (essential for diagnosis) 1
   • Aerobic and anaerobic cultures (withhold antibiotics for ≥2 weeks prior if medically stable) 1
   • Alpha-defensin testing (sensitivity 97%, specificity 96%; when combined with synovial CRP: sensitivity 97%, specificity 100%) 1, 5

3. Obtain plain radiographs to assess for loosening, osteolysis, or component migration 1, 6.

4. Assess clinical presentation systematically:

   • Night pain or rest pain suggests infection (versus weight-bearing pain suggesting mechanical loosening) 1, 6
   • Presence of sinus tract or persistent wound drainage confirms infection 1
   • Chronic infections may present with pain alone without fever, erythema, or warmth 1, 6

Critical Pitfall to Avoid

Do not rely on peripheral WBC count—it is not elevated in most patients with infected prostheses and cannot exclude infection 1, 6.

Surgical Decision Algorithm for Implant Removal

Debridement and Retention Strategy (Implant Preserved)

Consider debridement with implant retention ONLY if ALL criteria are met 1:

• Symptoms present <3 weeks OR implant age <30 days
• Well-fixed prosthesis confirmed on imaging
• Absence of sinus tract
• Organism susceptible to oral antimicrobial agents with biofilm activity

If these criteria are not met, implant removal is required 1.

Implant Removal Strategies

With CRP >200 mg/L, you are almost certainly dealing with established infection requiring implant removal. The surgical approach depends on 1:

1. Two-stage exchange (preferred for most cases):

   • Remove infected prosthesis
   • Place antibiotic-impregnated spacer
   • Administer pathogen-specific IV antibiotics for 2-6 weeks
   • Reimplant after infection clearance (confirmed by normalized inflammatory markers)

2. One-stage exchange (selected cases with known organism and adequate soft tissue)

3. Permanent removal without reimplantation (salvage for failed revisions or poor surgical candidates)

Antimicrobial Therapy Requirements

For staphylococcal infections (most common in implant infections) 1, 7:

• 2-6 weeks IV pathogen-specific therapy PLUS rifampin 300-450 mg orally twice daily
• Followed by rifampin plus oral companion drug (ciprofloxacin or levofloxacin) for total duration of 3 months (hip) or 6 months (knee)
• Rifampin must always be combined with another agent to prevent resistance 1, 7

Key Clinical Pearls

• Interleukin-6 combined with CRP provides superior diagnostic accuracy compared to traditional markers and should be obtained if available 1, 5.

• Implant-associated infections are typically monomicrobial with skin commensals (coagulase-negative staphylococci, Propionibacterium) or S. aureus 7, 4.

• The ultimate surgical decision must be made by the orthopedic surgeon with infectious disease consultation 1.

• A CRP of 200 mg/L with confirmed infection almost always necessitates implant removal, as debridement and retention has high failure rates outside the narrow criteria above 1.