What is the treatment for knee septic bursitis?

Treatment of Knee Septic Bursitis

The treatment of knee septic bursitis requires prompt antibiotic therapy targeting Staphylococcus aureus (which causes >80% of cases), combined with drainage through either serial needle aspirations or surgical intervention, with treatment duration based on clinical response and culture results. 1, 2

Diagnosis

• Suspect septic bursitis in patients with:

  • Acute knee pain and swelling
  • Erythema and warmth over the bursa
  • Fever (may be absent in some cases)
  • History of trauma, occupational kneeling, or immunocompromise
  • Characteristic bursal swelling that is distinct from septic arthritis

• Diagnostic approach:

  • Aspiration of bursal fluid for cell count, Gram stain, and culture
  • Bursal fluid leukocytosis >1000 cells/mm³ suggests infection 3
  • Blood cultures if systemic symptoms are present

Treatment Algorithm

Step 1: Initial Assessment and Decision for Outpatient vs. Inpatient Treatment

Indications for hospitalization:

• Presence of fulminant local infection
• Evidence of systemic toxicity (fever, hypotension)
• Immunocompromised patient
• Extensive infection
• Failed outpatient therapy 1

Step 2: Antimicrobial Therapy

Empiric antibiotic selection:

• Target Staphylococcus aureus as the most common pathogen (>80% of cases) 1
• First-line options:
  • For outpatients: Oral anti-staphylococcal antibiotics (dicloxacillin, cephalexin, or trimethoprim-sulfamethoxazole if MRSA is suspected)
  • For inpatients: IV nafcillin, cefazolin, or vancomycin if MRSA is suspected 4

Duration of therapy:

• Continue antibiotics for 5 days after documented culture sterility (typically 10-14 days total) 2
• Longer duration may be needed if symptoms were present for >2 weeks before treatment initiation 2

Step 3: Drainage Procedures

Options include:

1. Serial needle aspirations:

   • Perform initial aspiration for diagnosis
   • Repeat aspirations as needed to remove purulent material
   • Most effective when initiated early in the course of infection 2

2. Continuous suction-irrigation system:

   • Consider for severe cases
   • Percutaneous placement of drainage tubes
   • Local irrigation with antibiotic solution
   • Shown to be effective with no complications or recurrences 5

3. Surgical intervention:

   • Consider if no improvement with conservative measures
   • Options include incision and drainage or bursectomy
   • Indicated for cases with extensive infection, loculations, or failure of needle drainage 1

Special Considerations

• Early treatment is critical: Delay in treatment correlates with prolonged culture positivity despite antibiotics (r = 0.68, P < 0.001) 2
• Empiric antibiotics without aspiration: May be reasonable for select patients with suspected septic olecranon bursitis, with 88% showing uncomplicated resolution in one study 6
• Monitoring: Follow patients clinically for resolution of erythema, warmth, and swelling
• Prevention: Address occupational factors and recommend protective padding for those at risk

Common Pitfalls to Avoid

1. Misdiagnosis as non-septic bursitis: Always consider infection in patients with bursal swelling, especially with risk factors 3
2. Inadequate drainage: Failure to remove purulent material can lead to treatment failure
3. Insufficient duration of antibiotics: Continue therapy for at least 5 days after culture sterility 2
4. Failure to adjust antibiotics based on culture results: Modify therapy once pathogen and sensitivities are known
5. Missing underlying systemic conditions: Evaluate for predisposing factors such as diabetes or immunosuppression

By following this approach with prompt diagnosis, appropriate antibiotics, and adequate drainage, most cases of septic knee bursitis can be successfully treated with complete resolution and prevention of complications.