Three days after total knee arthroplasty, a patient presents with new erythema, warmth, pain, swelling, and tachycardia—what is the appropriate workup and management?

Emergency Department Workup for Suspected Early Periprosthetic Joint Infection

This patient requires immediate joint aspiration with synovial fluid analysis, ESR, CRP, and blood cultures—early postoperative infection (3 days post-TKA) with systemic signs demands urgent diagnosis and surgical consultation for potential debridement with implant retention. 1, 2, 3

Immediate Laboratory Workup

Serum Inflammatory Markers

• Obtain ESR and CRP immediately before any antibiotics are administered—when both are negative, infection is unlikely, but positive results warrant immediate aspiration 1, 4, 2
• CRP >13.5 mg/L has 73-91% sensitivity and 81-86% specificity for prosthetic knee infection 4, 2, 3
• Consider adding serum interleukin-6, which demonstrates higher predictive value than most other serologic markers when combined with CRP 1, 2
• Do not rely on peripheral WBC count—it is typically normal in prosthetic joint infections and is meaningless for excluding infection 4, 3

Blood Cultures

• Obtain blood cultures immediately given the tachycardia and systemic presentation—acute hematogenous infection is a critical differential at this early timepoint 5, 6

Joint Aspiration Protocol

Timing and Technique

• Proceed immediately with image-guided knee joint aspiration—this is the most useful diagnostic tool and should not be delayed 1, 2, 3
• Withhold antibiotics until after aspiration if the patient is hemodynamically stable to avoid false-negative cultures 2, 3
• Consider fluoroscopic or ultrasound guidance for accuracy 4

Synovial Fluid Analysis

• Send aspirate for: total and differential cell counts, aerobic and anaerobic bacterial cultures, alpha-defensin, synovial fluid CRP, and crystal analysis 1, 2, 3
• Alpha-defensin testing demonstrates 97% sensitivity and 96% specificity for periprosthetic joint infection, nearly matching the gold standard diagnostic criteria 1
• A "dry tap" does not exclude infection—if aspiration yields no fluid and clinical suspicion remains high, repeat aspiration is indicated 1, 2

Imaging

Plain Radiographs

• Obtain weight-bearing AP, lateral, and axial knee views to evaluate for periprosthetic lucency, component loosening, or fracture 1, 4, 3
• Radiographs are neither sensitive nor specific for infection at this early stage (3 days post-op) but are essential to exclude mechanical complications 1

Clinical Assessment Priorities

High-Specificity Clinical Signs

• Fever and erythema are highly specific findings with positive likelihood ratios of 10.78 and 8.08 respectively—their presence strongly supports infection diagnosis 7
• Joint effusion has a positive likelihood ratio of 2.42 for infection 7
• Night pain or pain at rest characteristically indicates infection, whereas pain on weight-bearing suggests mechanical loosening 4, 2, 3

Critical Pitfall

• Do not rely on absence of fever, erythema, or warmth to exclude infection—chronic infections frequently present with pain alone, but at 3 days post-op with systemic signs, this patient's presentation is highly concerning for acute infection 2, 3

Microbiological Considerations

Expected Pathogens

• Staphylococcus aureus and coagulase-negative Staphylococcus species are the most common organisms causing post-TKA infection 2, 5
• In acute hematogenous infections, Streptococcus species are also common and have better treatment outcomes than staphylococcal infections 5

Surgical Consultation

Immediate Orthopedic Involvement

• Contact orthopedic surgery immediately—early postoperative infections (within 3 weeks) are typically managed with debridement, antibiotics, and implant retention (DAIR) if diagnosed and treated promptly 6, 8
• The success of DAIR depends critically on early intervention—delays beyond symptom onset significantly worsen outcomes 5, 6
• Multi-disciplinary team discussion is essential for optimal management 1, 8

Diagnostic Algorithm Summary

1. Obtain ESR, CRP, blood cultures immediately (before antibiotics if hemodynamically stable) 1, 2
2. Perform urgent joint aspiration with comprehensive synovial fluid analysis including alpha-defensin 1, 2, 3
3. Obtain plain radiographs to exclude mechanical complications 1, 4
4. Consult orthopedic surgery emergently for potential surgical debridement 6, 8
5. Withhold antibiotics until cultures obtained unless patient is septic 2, 3

Risk Stratification

This patient has high probability of infection given:

• Presentation within 3 days of surgery (early postoperative period) 6
• Systemic signs (tachycardia) suggesting bacteremia 5
• Local inflammatory signs (erythema, warmth, swelling) with high specificity for infection 7