Septic Arthritis: Clinical Presentation and Management
Symptoms and Clinical Presentation
Septic arthritis presents with acute onset of monoarticular joint pain, swelling, erythema, warmth, and restricted mobility—this triad of fever, pain, and diminished mobility occurs in just over 50% of acute cases, making clinical suspicion paramount. 1, 2
Cardinal Symptoms
- Acute joint pain and swelling (typically single joint involvement) 3, 4
- Joint warmth and erythema with inability to bear weight on the affected limb 1, 5
- Fever >101.3°F (38.5°C) though constitutional symptoms like fever, chills, and rigors are poorly sensitive and may be absent 1, 5
- Restricted range of motion and joint immobility due to pain 1, 2
Most Commonly Affected Joints
- Knee and hip joints are most frequently involved 1, 2
- Hip involvement requires particular vigilance as it constitutes a surgical emergency 1
Key Clinical Predictors (Kocher Criteria for Hip)
The following criteria increase likelihood of septic arthritis when multiple are present: 1
- Fever >101.3°F
- Erythrocyte sedimentation rate (ESR) ≥40 mm/hour
- White blood cell count ≥12,000 cells/mm³
- Inability to bear weight on affected side
- C-reactive protein >2.0 mg/dL is an accurate additional predictor 1
Meeting all four Kocher criteria approaches 100% likelihood of septic arthritis. 1
Diagnostic Approach
Joint aspiration with synovial fluid analysis is the definitive diagnostic procedure and must be performed before initiating antibiotics whenever possible. 2, 6
Synovial Fluid Analysis
- White blood cell count ≥50,000 cells/mm³ is highly suggestive of septic arthritis 2, 6
- Synovial fluid culture is positive in approximately 80% of non-gonococcal cases 2, 6
- Gram stain should be performed immediately to guide initial antibiotic selection 3, 5
- Crystal analysis should be obtained as crystal arthropathy can occasionally coexist with infection 5
Laboratory Markers
- Elevated CRP and ESR support the diagnosis but are nonspecific 6, 3
- Blood cultures should be obtained before antibiotic initiation 7
- Elevated peripheral WBC count with neutrophil predominance 1, 6
Imaging
- Ultrasound is the initial imaging modality of choice, especially for hip joints, to detect effusions and guide aspiration 6
- Plain radiographs have low sensitivity but help exclude fractures and other conditions 6, 7
- MRI has high sensitivity for detecting joint effusions, soft tissue involvement, and concomitant osteomyelitis when clinical suspicion remains high 6
Treatment Protocol
Septic arthritis is an orthopedic emergency requiring immediate surgical drainage combined with intravenous antibiotic therapy to prevent irreversible cartilage damage. 1, 2, 6
Surgical Management (First-Line)
- Immediate surgical debridement is essential through arthrotomy, irrigation, and debridement 2, 6
- Surgical drainage is indicated in all cases of septic arthritis 1, 2
- Hip joint involvement requires open surgical drainage 1
- Arthroscopic drainage may be appropriate for accessible joints 6
Empiric Antibiotic Therapy
Start IV vancomycin immediately after obtaining cultures to cover MRSA, which is increasingly common in septic arthritis. 2, 6, 7
Adult Regimen
- IV vancomycin as first-line therapy for MRSA coverage 2, 6, 7
- Adding rifampin 600 mg daily or 300-450 mg twice daily may be beneficial for better bone and biofilm penetration 2, 6
- For gram-negative cocci: ceftriaxone 5
- For gram-negative rods: ceftazidime 5
- If Gram stain negative but high clinical suspicion: vancomycin plus ceftazidime or aminoglycoside 5
Pediatric Regimen
- IV vancomycin for MRSA coverage 2, 6
- Clindamycin 10-13 mg/kg/dose IV every 6-8 hours as alternative if local clindamycin resistance is low 2, 6
Pathogen-Specific Considerations
- Staphylococcus aureus is the most common pathogen across all age groups 1, 3
- Kingella kingae should be considered in children <4 years of age 1, 2, 6
- Salmonella species in patients with sickle cell disease 1, 2, 6
- Group B streptococcus in neonates 1
Duration of Therapy
- 3-4 weeks for uncomplicated septic arthritis 2, 6, 7
- Concomitant osteomyelitis (occurs in up to 30% of cases) requires longer treatment 2, 6, 7
- Prosthetic joint infections require 12 weeks of antibiotics for better outcomes 2, 6
Transition to Oral Antibiotics
- Oral antibiotics can be given in most cases as they are not inferior to IV therapy 3
- Transition only after clinical improvement and resolution of systemic inflammatory response 7
Special Populations and Scenarios
Prosthetic Joint Infection
- Device removal is recommended in all cases 1, 2
- If device cannot be removed: chronic suppression with fluconazole 400 mg daily (for Candida) if isolate is susceptible 1, 2
- Two-stage revision with 3-6 months between resection and reimplantation 1
Polymicrobial Infections
- Dual antibiotic coverage is necessary for polymicrobial infections 2, 6
- Mixed infections with bacteria, especially Staphylococcus aureus, are not uncommon 1
Persistent or Recurrent Symptoms
- Re-treatment with another 4-week course of oral antibiotics or 2-4 weeks of IV ceftriaxone for persistent joint swelling after initial treatment 2, 6
- Arthroscopic synovectomy may reduce duration of joint inflammation in cases of persistent synovitis with significant pain or functional limitation 6
Critical Pitfalls to Avoid
- Negative joint aspirate culture does not rule out infection—consider percutaneous bone biopsy if clinical suspicion remains high 2, 6
- Do not delay treatment waiting for culture results if clinical suspicion is high 7, 3
- Concomitant osteomyelitis is frequently missed—maintain high suspicion and consider MRI if treatment response is suboptimal 2, 6, 7
- Patients meeting SIRS criteria require hospital admission—outpatient management is inappropriate due to risk of rapid deterioration 7
- Monitor for drug interactions and adverse effects in elderly patients receiving prolonged antibiotic therapy 6
Prognosis and Outcomes
- Poor functional outcomes occur in 24-33% of patients, including amputation, arthrodesis, or severe functional deterioration 4
- 90-day mortality rate is 7% in patients ≤79 years and 22-69% in patients >79 years for knee septic arthritis 4
- Delays in diagnosis and treatment result in permanent morbidity and mortality 8, 9, 3