What is the most appropriate initial management for a post-knee replacement surgery patient with fever, leukocytosis, and radiographic evidence of right lower lobe infiltration?

Initial Management: Broad-Spectrum Antibiotics

The most appropriate initial management is B - broad-spectrum antibiotics, but only after obtaining blood cultures, inflammatory markers (ESR, CRP, interleukin-6), and performing knee joint aspiration for synovial fluid analysis. 1, 2

Critical Diagnostic Steps Before Antibiotic Administration

The clinical presentation—fever (38°C), leukocytosis (WBC 15,000), and right lower lobe infiltrate on chest X-ray in a post-knee replacement patient—suggests two concurrent problems: postoperative pneumonia AND possible occult periprosthetic joint infection (PJI).

Why Joint Aspiration Must Come First

• The American Academy of Orthopaedic Surgeons strongly recommends obtaining ESR, CRP, and serum interleukin-6 immediately to evaluate for occult PJI in any post-TKR patient with concerning symptoms. 1, 2
• Knee joint aspiration for synovial fluid analysis should be performed before initiating antibiotics, as this is critical for identifying causative organisms in PJI. 2
• Withhold antibiotics for at least 2 weeks prior to aspiration when clinically feasible to avoid false-negative cultures, though in this acute scenario with pneumonia, you must balance this against the need to treat the pulmonary infection. 1, 2
• Peripheral WBC count of 15,000 is meaningless for excluding or confirming PJI—most patients with infected prostheses have normal peripheral WBC counts. 1, 2

The Pneumonia Component

• The presence of fever, leukocytosis, and right lower lobe infiltrate meets criteria for hospital-acquired pneumonia (HAP) requiring empiric broad-spectrum antibiotics. 3
• A new or progressive radiographic infiltrate plus at least two of three clinical features (fever >38°C, leukocytosis, and purulent secretions) represent the most accurate clinical criteria for starting empiric antibiotic therapy. 3
• Blood cultures should be obtained before antibiotic administration to identify causative organisms. 3

Recommended Management Algorithm

1. Immediately obtain: Blood cultures, ESR, CRP, serum interleukin-6, and knee radiographs 1, 2
2. Perform knee joint aspiration for synovial fluid analysis (cell count, differential, Gram stain, culture) before antibiotics if the patient is stable enough for a brief delay 1, 2
3. Initiate broad-spectrum antibiotics covering both HAP pathogens (including Staphylococcus aureus and gram-negative organisms) and potential PJI organisms 3, 2
4. Obtain sputum cultures if productive cough is present 3
5. Reassess by Day 3 based on culture results and clinical response, narrowing antibiotic spectrum as appropriate 3

Why Other Options Are Inadequate

• IV fluids (Option A): While supportive care is important, fluids alone do not address the underlying infections (pneumonia ± PJI) that are driving the fever and leukocytosis. 3
• Antipyretics (Option C): Treating fever symptomatically without addressing the infectious source is dangerous and delays definitive management. 3
• DVT prophylaxis (Option D): While important in post-surgical patients, this does not address the acute infectious process. The clinical picture points to infection, not thromboembolism. 3

Critical Pitfalls to Avoid

• Do not rely on the absence of knee pain, erythema, or warmth to exclude PJI—chronic infections frequently present with pain alone or may be completely occult. 1, 2
• Do not assume the pneumonia is the only problem—the post-TKR setting demands evaluation for PJI even when another infection source is apparent. 1, 2
• CRP has 73-91% sensitivity and 81-86% specificity for prosthetic knee infection when using a cutoff of 13.5 mg/L, making it far more reliable than WBC count. 1, 2
• If inflammatory markers are elevated or joint aspiration shows elevated WBC (>16,200/μL), infection is highly likely and requires aggressive management. 2, 4