What is the recommended treatment for a septic knee?

Treatment for Septic Knee

Septic arthritis of the knee is an orthopedic emergency requiring immediate surgical drainage and prompt administration of broad-spectrum antibiotics within one hour of diagnosis, followed by a 3-4 week course of pathogen-directed antimicrobial therapy. 1, 2

Initial Management

• Septic arthritis of the knee is considered an orthopedic emergency as bacterial proliferation can rapidly cause cartilage damage 1
• Obtain joint fluid and blood cultures before starting antibiotics, but do not delay treatment more than 45 minutes 1, 2
• Administer broad-spectrum IV antibiotics within one hour of diagnosis to cover all likely pathogens 1, 2
• Each hour of delay in antibiotic administration increases morbidity and mortality 1, 2

Surgical Intervention

• Drainage or debridement of the joint space should always be performed as the mainstay of therapy 1, 2
• Options include arthrocentesis, arthroscopic drainage, or open arthrotomy depending on severity and local expertise 3
• The Gächter classification can help establish prognosis and determine the need for extensive debridement 3
• Consider repeat surgical drainage if there is poor clinical response to initial treatment 1, 2

Antibiotic Therapy

• Initial empiric antibiotics should include:
  • IV vancomycin (15-20 mg/kg/dose every 8-12 hours) for MRSA coverage 1, 2
  • Plus a second agent for gram-negative coverage, such as a third-generation cephalosporin or fluoroquinolone 1, 2
• Staphylococcus aureus is the most common pathogen in septic arthritis 3, 4
• Duration of therapy:
  • 3-4 weeks for uncomplicated septic arthritis 1, 2
  • 4-6 weeks for patients with slow clinical response or evidence of osteomyelitis 1, 5
• Narrow antibiotic therapy once pathogen identification and sensitivities are established 1
• Empiric combination therapy should not be administered for more than 3-5 days 1

Pathogen-Specific Considerations

• For MRSA infections: IV vancomycin is the first-line treatment 1, 2
• For Pseudomonas aeruginosa: combination therapy with a beta-lactam and either an aminoglycoside or fluoroquinolone 1
• For Streptococcus pneumoniae: a combination of beta-lactam and macrolide is recommended 1
• For gram-negative cocci (including Neisseria gonorrhoeae): ceftriaxone is appropriate 6
• For gram-negative rods: ceftazidime is recommended 6

Monitoring and Follow-up

• Perform clinical examinations several times per day to assess response to treatment 1, 2
• Monitor inflammatory markers (ESR, CRP) to guide response to therapy 1, 2
• Begin early mobilization when inflammation resolves to prevent joint stiffness 1, 2

Common Pitfalls and Special Considerations

• Delayed diagnosis and treatment significantly worsen outcomes - each hour delay in antibiotic administration increases mortality 1, 2
• Risk factors for septic arthritis include age >60 years, diabetes mellitus, rheumatoid arthritis, recent joint surgery, prosthetic joints, skin infection, and immunosuppression 3, 4
• Crystal arthropathy and septic arthritis can occasionally coexist - don't rule out infection based solely on crystal presence 6
• Prosthetic joint infections require different management strategies with potentially longer antibiotic courses 1, 6
• Patients with gouty arthritis have a higher risk of developing septic arthritis (43.5% in one study) 7