Treatment of Septic Arthritis
The treatment of septic arthritis requires immediate joint drainage (either through arthrocentesis, arthroscopic lavage, or open surgical drainage) combined with appropriate antibiotic therapy, typically starting with empiric coverage against Staphylococcus aureus including MRSA, followed by targeted antibiotics based on culture results. 1
Diagnostic Approach
Initial Evaluation
- Obtain synovial fluid for analysis before starting antibiotics whenever possible
- Send fluid for:
- Cell count and differential (WBC >50,000 cells/mm³ with >90% neutrophils suggests septic arthritis)
- Gram stain
- Culture and sensitivity
- Crystal analysis to rule out crystal arthropathy
Imaging
- Plain radiographs: Establish baseline and exclude fractures or tumors
- Ultrasound: High sensitivity for detecting joint effusions and guiding aspiration
- MRI with contrast: Indicated when joint aspiration is inconclusive or to evaluate infection extent beyond joint space 1
- CT with IV contrast: Alternative if MRI is contraindicated 1
Treatment Algorithm
1. Joint Drainage
- Mandatory first step: Prompt evacuation of purulent material 2
- Options include:
- Arthrocentesis at bedside (for accessible joints)
- Arthroscopic drainage (preferred for most joints)
- Open surgical drainage (for difficult access or complicated cases)
- Image-guided drainage (ultrasound or CT-guided) 3
- Septic joints require immediate surgical debridement and intraoperative cultures, as the absence of a protective basement membrane within the joint lining results in bacteremia in approximately 70% of cases 3
2. Antimicrobial Therapy
Empiric Therapy
Adults:
Children:
- IV vancomycin is recommended for acute hematogenous MRSA osteomyelitis and septic arthritis 3
- If patient is stable without ongoing bacteremia, clindamycin 10-13 mg/kg/dose IV every 6-8 hours can be used if local clindamycin resistance rate is low (<10%) 3
- Duration: 3-4 weeks for septic arthritis, 4-6 weeks if concurrent osteomyelitis 3
Targeted Therapy
- Adjust antibiotics based on culture and sensitivity results
- For MRSA infections:
- For methicillin-sensitive S. aureus:
- Switch to nafcillin, oxacillin, or cefazolin
- For gram-negative organisms:
- Appropriate antibiotics based on sensitivity (ceftriaxone, fluoroquinolones, etc.) 5
3. Adjunctive Measures
- Initial joint immobilization for pain control
- Early range of motion exercises once pain improves
- Monitor inflammatory markers (CRP, ESR) to assess treatment response 1
- Regular clinical reassessment for improvement
Special Considerations
Prosthetic Joint Infections
- Require specialized management with longer antibiotic courses
- Often require hardware removal or exchange 1
- Lower threshold for diagnosis: intraarticular cutoff values as low as 1,100 WBC/mm³ with neutrophil differential >64% 1
Concurrent Osteomyelitis
- Common in pediatric septic arthritis
- Requires extended antibiotic therapy (6 weeks) 2
- MRI with contrast is highly sensitive for detection 1
Risk Factors for Treatment Failure
- Rheumatoid arthritis
- Synovial WBC levels >10.5 × 10⁹ cells/L
- Delayed treatment
- Immunocompromised state 6
Pitfalls to Avoid
- Delaying joint drainage while waiting for antibiotics to work
- Failing to obtain cultures before starting antibiotics
- Missing concurrent osteomyelitis, especially in pediatric patients
- Inadequate duration of antibiotics
- Premature discontinuation of antibiotics based on clinical improvement alone without monitoring inflammatory markers
By following this structured approach with prompt joint drainage and appropriate antibiotic therapy, most patients with septic arthritis can achieve full recovery with preserved joint function.