Workup and Treatment for Septic Arthritis
Septic arthritis requires immediate joint drainage through arthrocentesis or surgical debridement, followed by appropriate antibiotic therapy for 3-4 weeks, with extension to 6 weeks if osteomyelitis is present. 1, 2
Diagnostic Workup
Clinical Assessment
- Acute onset of monoarticular joint pain, erythema, heat, and immobility
- Constitutional symptoms (fever, chills) are poorly sensitive for septic arthritis 3
- Risk factors: age >80 years, diabetes mellitus, rheumatoid arthritis, recent joint surgery, prosthetic joints, skin infection, immunosuppression 4
Laboratory Studies
- Inflammatory markers: ESR, CRP (elevated but nonspecific) 4
- Blood cultures (positive in 50-70% of cases)
Joint Aspiration (Essential)
- Synovial fluid analysis:
Imaging
- Radiography: initial imaging to assess for joint effusion, gas formation, osteomyelitis
- MRI: preferred for detecting early osteomyelitis, soft tissue involvement, and abscess formation 1
- Ultrasound: useful for guided aspiration and detecting effusions
Treatment Algorithm
Step 1: Determine if Surgical Emergency
- If clinical presentation suggests septic arthritis with severe symptoms or unstable patient:
- Proceed directly to surgical debridement with intraoperative cultures 1
- If non-emergency:
- Perform joint aspiration for diagnosis 1
Step 2: Joint Drainage
- All cases require evacuation of purulent material 3
- Options:
- Arthrocentesis (for accessible joints without complications)
- Surgical drainage (arthroscopic or open) for:
- Hip joints
- Inadequate response to arthrocentesis
- Loculated effusions
- Presence of adjacent osteomyelitis
Step 3: Empiric Antibiotic Therapy
- Start immediately after obtaining synovial fluid 4
- Initial selection based on Gram stain results:
Step 4: Definitive Antibiotic Therapy
- Adjust based on culture and sensitivity results
- For MRSA:
- Vancomycin IV or
- Daptomycin 6 mg/kg/day IV once daily or
- Linezolid 600 mg PO/IV twice daily 2
- Consider adding rifampin for improved outcomes in MRSA infections 1, 5
Step 5: Transition to Oral Therapy
- After clinical improvement and normalization of inflammatory markers
- Choose antibiotics with good bioavailability:
- Fluoroquinolones (for susceptible gram-negative organisms)
- Linezolid, clindamycin, or TMP-SMX (for susceptible gram-positive organisms) 2
- Avoid oral β-lactams due to low bioavailability 2
Step 6: Duration of Therapy
- Uncomplicated septic arthritis: 3-4 weeks 1, 2
- With osteomyelitis: 4-6 weeks 2, 6
- With prosthetic joint infection: 6 weeks or longer 2
Special Considerations
Prosthetic Joint Infections
- Lower threshold for diagnosis (>1,100 WBCs/mm³ with >64% neutrophils) 3
- May require device removal or retention based on timing and stability 1
- For early-onset infections with stable implants: parenteral therapy plus rifampin for 2 weeks, followed by rifampin plus another oral agent for 3-6 months 1
Pediatric Considerations
- Distribution varies by age: children <2 years more likely to have septic arthritis than osteomyelitis 1
- Kocher criteria for hip joint: fever >101.3°F, ESR ≥40 mm/hr, WBC ≥12,000 cells/mm³, inability to bear weight 1
- CRP >2.0 mg/dL is an accurate predictor of septic arthritis in children 1
Monitoring and Follow-up
- Regular assessment of clinical response
- Monitor inflammatory markers (ESR, CRP) for normalization
- Repeat joint aspiration if clinical improvement is inadequate
- Consider repeat imaging if osteomyelitis is suspected or if there's poor response to treatment