What are the investigation and management steps for septic arthritis?

Investigation and Management of Septic Arthritis

Septic arthritis is an orthopedic emergency requiring immediate surgical debridement combined with appropriate antibiotic therapy for at least 4 weeks to prevent joint destruction and reduce risk of relapse. 1, 2

Diagnostic Approach

Clinical Evaluation

• Consider septic arthritis in patients presenting with acute monoarticular pain, especially in the hip joint 3
• The Kocher criteria help distinguish septic arthritis from other conditions, particularly in pediatric patients, and include: fever, elevated ESR (≥40 mm/hour), elevated white blood cell count, and inability to bear weight on the affected limb 4
• C-reactive protein >2.0 mg/dL is an additional predictor of septic arthritis 4

Laboratory Investigations

• Joint aspiration is the definitive diagnostic procedure with synovial fluid white blood cell count ≥50,000 cells/mm³ strongly suggestive of septic arthritis 1
• Blood cultures should be obtained before initiating antibiotics to identify potential hematogenous spread 1
• Synovial fluid should be sent for Gram stain, culture, crystal analysis (to rule out crystalline arthropathy), and cell count 1
• ESR and CRP are important inflammatory markers; normal ESR values should prompt reconsideration of septic arthritis diagnosis 4

Imaging Studies

• Ultrasound is recommended as the initial imaging modality, especially for hip joints, to detect effusions and guide aspiration 3
• Plain radiographs have low sensitivity but may help rule out other conditions 3
• MRI has high sensitivity for detecting joint effusions, soft tissue involvement, and concomitant osteomyelitis when clinical suspicion remains high despite negative joint aspiration 3, 1

Management Algorithm

Surgical Intervention

• Immediate surgical debridement is the standard of care for septic arthritis 1, 5
• Arthrotomy with irrigation and debridement is the traditional approach, though arthroscopic techniques may be used for certain joints 1, 6
• Medical treatment with repeated arthrocentesis may be considered in select cases, potentially resulting in shorter hospital stays and better functional outcomes, though this remains controversial 6

Antimicrobial Therapy

• Antibiotic therapy should be administered for at least 4 weeks to reduce risk of relapse 2
• Initial empiric therapy should cover the most likely pathogens based on patient age and risk factors:
  • For adults: IV vancomycin is recommended as first-line therapy 1
  • For children <4 years: Coverage for Kingella kingae should be included 7, 1
  • For patients with sickle cell disease: Coverage for Salmonella species is necessary 7, 1
  • For IV drug users: Broad coverage including MRSA is essential 7
• Adjust antibiotics based on culture results and susceptibility testing 1
• Consider adding rifampin for MRSA infections due to its excellent penetration into bone and biofilm 1

Special Considerations

• Concomitant osteomyelitis occurs in up to 30% of children with septic arthritis and requires longer treatment 1
• Polymicrobial infections require broader antimicrobial coverage 7, 1
• In cases of persistent or recurrent joint swelling after a course of antibiotics, consider re-treatment with another 4-week course of oral antibiotics or 2-4 weeks of IV antibiotics 1
• For prosthetic joint infections, longer antibiotic courses (12 weeks) show better outcomes than shorter courses 1

Monitoring and Follow-up

• Monitor clinical response, inflammatory markers (ESR, CRP), and joint function 4
• Early physical therapy is recommended to prevent joint stiffness and muscle atrophy 8
• Vigilant monitoring for relapse is essential, particularly in patients with risk factors such as synovial fluid WBC counts ≥150 × 10³/mm³ at diagnosis 2

Pitfalls and Caveats

• Negative joint aspirate culture does not rule out infection; consider percutaneous bone biopsy if clinical suspicion remains high 1
• Delay in diagnosis and treatment can lead to irreversible joint damage and increased mortality 5
• Certain joints like the sternoclavicular joint may present with more insidious onset, requiring a high index of suspicion 9
• Intra-articular corticosteroid injections are contraindicated during active infection 1
• Bacterial proliferation within the joint space leads to rapid cartilage damage through direct toxicity and inflammatory response, making prompt treatment crucial 7