Management of High Fever and Acute Knee Joint Pain
This patient requires immediate arthrocentesis to rule out septic arthritis before any other intervention, as a delay in diagnosis and treatment can result in permanent morbidity and mortality. 1
Immediate Diagnostic Workup
The acute onset of monoarticular knee pain with high fever (103°F) is septic arthritis until proven otherwise. 1, 2
Essential Laboratory Tests
- Obtain ESR and CRP immediately - the combination provides 93% sensitivity, 100% specificity, and 97% accuracy when at least 2 of 3 tests are abnormal 3
- Blood cultures for aerobic and anaerobic organisms should be obtained given the presence of fever 3
- Plain radiograph of the knee should be performed 3
Synovial Fluid Analysis (Critical Step)
Perform arthrocentesis urgently - this is the definitive diagnostic test and must be done before initiating antibiotics if the patient is stable enough to wait. 3, 1, 2
The synovial fluid must be analyzed for:
- Total cell count and differential leukocyte count (septic arthritis typically shows >50,000 WBC/mm³ in the absence of peripheral leukopenia) 2
- Gram stain to guide initial antibiotic selection 1, 2
- Aerobic and anaerobic bacterial cultures 3, 1
- Crystal analysis to exclude coexisting crystal arthropathy 2
Empiric Antibiotic Therapy
If there is strong clinical concern for septic arthritis after obtaining synovial fluid, initiate empiric antibiotics immediately - do not wait for culture results. 3, 1
Antibiotic Selection Based on Gram Stain
- Gram-positive cocci: Vancomycin 2
- Gram-negative cocci: Ceftriaxone 2
- Gram-negative rods: Ceftazidime 2
- Negative Gram stain with strong clinical suspicion: Vancomycin plus ceftazidime or an aminoglycoside 2
Staphylococcus aureus is the most common pathogen isolated in septic arthritis, accounting for over 80% of nongonococcal cases. 1, 2
Route and Duration
- Oral antibiotics are not inferior to intravenous therapy and can be given in most cases 1
- Total duration ranges from 2-6 weeks depending on the organism and clinical response 1
Joint Drainage
Evacuation of purulent material is necessary through either repeated arthrocentesis or surgical drainage. 2
Critical Pitfalls to Avoid
Do Not Rely on Constitutional Symptoms
Fever, chills, and rigors are poorly sensitive for septic arthritis - their absence does not exclude the diagnosis. 2 The patient's high fever in this case increases suspicion but is not always present.
Do Not Delay Antibiotics for Culture Results
If synovial fluid has been obtained and there is clinical concern for septic arthritis, withholding antibiotics while awaiting culture results increases morbidity and mortality. 3, 1
Consider Alternative Diagnoses Only After Excluding Infection
While brucellosis can cause septic arthritis affecting large joints like the knee with fever 3, and crystal arthropathies can coexist with infection 2, infection must be definitively ruled out first as it represents the greatest immediate threat to joint integrity and life.
Special Consideration for Risk Factors
This patient's risk factors should be assessed, as age >80 years, diabetes mellitus, rheumatoid arthritis, recent joint surgery, prosthetic joints, skin infection, and immunosuppressive medications all increase septic arthritis risk. 1