What is the recommended management for a suspected septic joint in an adult?

Management of Suspected Septic Joint in Adults

Immediately perform joint aspiration (with image guidance for hip/shoulder) and initiate empiric IV vancomycin 15 mg/kg every 6 hours after obtaining synovial fluid and blood cultures, followed by urgent surgical drainage within 24 hours. 1, 2

Initial Diagnostic Approach

Clinical Recognition

• Suspect septic arthritis in any patient with acute monoarticular joint pain, swelling, and fever, though this classic triad occurs in only 50% of cases 1
• Meeting all five diagnostic criteria approaches 100% likelihood: fever >101.3°F, ESR ≥40 mm/hour, WBC ≥12,000 cells/mm³, inability to bear weight, and CRP >2.0 mg/dL 1
• Risk factors include age >80 years, diabetes, rheumatoid arthritis, recent joint surgery, prosthetic joints, skin infection, and immunosuppressive medications 3

Imaging Algorithm

• Obtain plain radiographs first to exclude fractures, tumors, and provide anatomic overview, though they have low sensitivity in early disease (<14 days) and may show only soft tissue swelling 1, 2
• Use ultrasound for hip joints to detect effusions (sensitivity 95% if symptoms >1 day) and guide aspiration—absence of hip effusion on ultrasound virtually excludes septic arthritis 1, 2
• For knee joints, bedside aspiration can be performed without imaging guidance 1

Definitive Diagnosis: Joint Aspiration

Aspiration Technique

• Perform joint aspiration immediately before initiating antibiotics whenever possible, using ultrasound or fluoroscopy guidance for hip/shoulder joints to ensure proper needle placement 1, 2
• Send synovial fluid for cell count with differential, Gram stain, and culture 4, 1
• Synovial fluid WBC ≥50,000 cells/mm³ is highly suggestive of septic arthritis, though lower counts do not exclude infection 1, 5
• Synovial fluid culture is positive in approximately 80% of non-gonococcal cases 1, 2

Critical Pitfalls

• A negative Gram stain does not exclude bacterial infection—proceed with empiric antibiotics if clinical suspicion is high 2
• A "dry tap" does not exclude infection—consider repeat aspiration or proceed to MRI 2
• Patients who received antibiotics before aspiration may have false-negative cultures; ideally, patients should be off antibiotics for 2 weeks before aspiration if clinically safe 2
• Always perform crystal analysis even when infection is suspected, as gout and septic arthritis can coexist in up to 27% of cases 1, 2

Empiric Antibiotic Therapy

Initial Treatment

• Start IV vancomycin 15 mg/kg every 6 hours (or 30-60 mg/kg/day in 2-4 divided doses) immediately after obtaining cultures to cover MRSA, which has become a major cause of septic arthritis 1, 2, 6
• Alternative empiric options if MRSA is less likely: linezolid 600 mg IV/PO every 12 hours, daptomycin 6 mg/kg IV daily, or teicoplanin 6-12 mg/kg IV every 12 hours for 3 doses then daily 2
• If Gram stain is negative but clinical suspicion is high, use vancomycin plus ceftazidime or an aminoglycoside for broad coverage 5

Culture-Directed Therapy

• For MSSA: switch to nafcillin/oxacillin 1-2 g IV every 4 hours, cefazolin 1 g IV every 8 hours, or clindamycin 600 mg IV every 8 hours if penicillin-allergic 2
• For MRSA: continue vancomycin and consider adding rifampin 600 mg PO daily or 300-450 mg PO twice daily for enhanced bone and biofilm penetration 2
• For Streptococcal infections: use penicillin G 20-24 million units IV daily or ceftriaxone 1-2 g IV every 24 hours 2

Surgical Drainage

Indications and Timing

• Surgical drainage is mandatory in all cases of septic arthritis—bacterial proliferation can cause irreversible cartilage damage within hours to days 1, 2, 6
• Drainage options include daily needle aspiration, arthroscopic drainage, or open arthrotomy 7
• Immediate surgical debridement is required for hip or shoulder involvement, symptoms >7 days, severe sepsis, or prosthetic joint infections 2
• Repeated needle aspiration alone fails in 46% of cases, making surgical drainage preferable for most patients 2

Special Considerations

• For prosthetic joint infections, device removal or debridement with retention plus prolonged antibiotics is necessary 2
• Image-guided drainage in radiology suite is an alternative when surgical expertise is limited 6

Treatment Duration and Route

Duration Guidelines

• Uncomplicated native joint septic arthritis: 3-4 weeks total, though recent high-quality evidence suggests 2 weeks may be adequate after surgical drainage for smaller joints 2
• The traditional 3-4 week duration remains more prudent for large joints (hip, knee, shoulder) 2
• Extend to 6 weeks if imaging evidence of concomitant osteomyelitis exists 6
• Prosthetic joint infections with debridement and retention: 12 weeks (superior to 6 weeks based on 2021 DATIPO trial) 2
• Prosthetic hip with exchange: 3 months; prosthetic knee with exchange: 6 months 2

Route of Administration

• Oral antibiotics are not inferior to IV therapy and can be initiated after 2-4 days if the patient is clinically improving, afebrile, and tolerating oral intake 1, 2, 3
• Oral options for MRSA (after initial IV therapy): linezolid 600 mg PO every 12 hours, TMP-SMX (trimethoprim 4 mg/kg/dose) PO every 8-12 hours plus rifampin 600 mg PO daily, or fusidic acid 500 mg PO every 8 hours plus rifampin 2

Role of MRI

When to Order MRI

• Order MRI with and without IV contrast when clinical suspicion remains high despite negative joint aspiration, concern exists for concurrent osteomyelitis (occurs in 30-58% of cases), or need to assess for soft tissue abscess/pyomyositis 4, 1, 2
• MRI has 82-100% sensitivity and 75-96% specificity for diagnosing septic arthritis and osteomyelitis 1, 2
• A negative MRI effectively excludes septic arthritis 1, 2
• Key MRI findings include joint effusion, synovial thickening/enhancement, bone marrow edema, periarticular soft tissue inflammation, and decreased femoral head enhancement on early post-contrast imaging 4, 1

Critical Limitations

• MRI should complement, not replace, joint aspiration—the 2022 ACR Appropriateness Criteria explicitly state insufficient evidence to support MRI as the initial imaging study 1
• Never delay antibiotics to obtain MRI—start vancomycin immediately after joint aspiration and blood cultures 2
• Over 50% of pediatric patients with septic arthritis have infection beyond the joint space on MRI, highlighting the importance of assessing for concurrent osteomyelitis 4, 1

Monitoring and Follow-up

Treatment Response

• Monitor CRP and ESR to assess treatment response—these should trend downward with appropriate therapy 1, 2
• Monitor vancomycin trough levels to adjust dosing and minimize toxicity 1
• Be vigilant for drug interactions and adverse effects, especially in elderly patients 2

Persistent or Worsening Symptoms

• If joint aspirate culture is negative but clinical suspicion remains high, consider percutaneous image-guided bone biopsy to evaluate for concurrent osteomyelitis 4, 1, 2
• Consider repeat MRI for worsening or persistent symptoms, which results in management changes in 21% of cases 1
• If cultures remain persistently negative despite appropriate treatment, consider synovial fluid alpha-defensin, leukocyte esterase, or nucleic acid amplification testing (PCR) for bacteria 2

Pathogen-Specific Considerations

Common Pathogens

• Staphylococcus aureus (including MRSA) is the most common pathogen in all age groups 1, 3, 5
• In neonates, Group B streptococcus predominates 1
• In children <4 years, Kingella kingae is common 1, 2
• In patients with sickle cell disease, consider Salmonella species 2
• Neisseria gonorrhoeae should be considered based on sexual history and risk factors 3

Polymicrobial Infections

• Dual antibiotic coverage is mandatory when multiple organisms are identified, for example, linezolid for MRSA plus ciprofloxacin for Pseudomonas aeruginosa 2