Septic arthritis

Background

• Most important diagnostic consideration in acute joint pain (can destroy joint in days)
• Knee most commonly involved in adults; hip most common in peds
• Most often seen in pts >65yr
• Most common causative organisms
  • <35 y/o N. gonorrhoeae
  • >35 y/o S. aureus

Clinical Features

• Fever
• Warm, red, painful, swollen joint
• Decreased range of motion to active and passive movement
• Gonococcal arthritis
  • Urethritis/vaginitis may be absent
  • may have prodromal phase:
    • Migratory arthritis and tenosynovitis predominate before pain and swelling occurs
    • Macularpapular rash or pustules esp on hands/feet may proceed overt arthritis
• Endocarditis should be considered in the presence of 2 or more affected joints

Diagnosis

Arthrocentesis of synoval fluid

Synovium	Normal	Noninflammatory	Inflammatory	Septic
Clarity	Transparent	Transparent	Cloudy	Cloudy
Color	Clear	Yellow	Yellow	Yellow
WBC	<200	<200-2000	200-50,000	>1,100 (prosthetic joint) >25,000; LR=2.9 >50,000; LR=7.7 >100,000; LR=28
PMN	<25%	<25%	>50%	>64% (prosthetic joint) >90%
Culture	Neg	Neg	Neg	>50% positive
Lactate	<5.6 mmol/L	<5.6 mmol/L	<5.6 mmol/L	>5.6 mmol/L
LDH	<250	<250	<250	>250
Crystals	None	None	Multiple or none	None

• Viscosity of synovial fluid may actually be decreased in inflammatory or infectious etiologies, as hyaluronic acid concentrations decrease
• The presence of crystals does not rule out septic arthritis; however, the diagnosis is highly unlikely with synovial WBC < 50,000

DDx

1. Toxic synovitis
2. Abscess
3. Cellulitis
4. Primary rheumatologic disorder (i.e. vasculitis)
5. Iatrogenic
6. Reactive arthritis (post-infectious)

Work-Up

1. Arthrocentesis with synovial fluid analysis
   1. Synovial fluid culture only (not 100% sensitive)
2. CBC
3. ESR
   1. Sn 94% (with 15mm/h cut-off)
4. CRP
   1. Sn 92% (with 20mg/L cut-off)
5. Blood Culture
6. Gonorrhea culture (urethral/cervical/pharyngeal/rectal)
7. Imaging
   1. Helpful for excluding other diagnoses (e.g. trauma, osteo)
8. Immunocompromised
   1. Consider mycobacterial or fungal arthritis

Arthrocentesis

• Treatment based on diagnostic studies

Antibiotics

For adults treatment should be divided into Gonococcal and Non-Gonococcal

Gonococcal

• Ceftriaxone 1g IV once daily
• Cefixime 400 mg PO BID is an option for outpatient therapy after initial 3 days of Ceftriaxone

Non-Gonococcal

• Treatment should cover S. aureus, Streptococcus, Pseudomonas, Enterococcus, B. burgdorferi
• Vancomycin 15-20 mg/kg IV BID PLUS any of the following:
  • Ceftriaxone 2g IV once daily
  • Cefepime 2g IV three times daily
  • Ceftazidime 2g IV three times daily
  • Ciprofloxacin 400mg IV three times daily

Pediatrics

• Ceftriaxone 1g IV once daily

Sickle Cell

Coverage for Salmonella and Staphylococcus spp

• Vancomycin 20mg/kg IV twice daily PLUS
  • Ciprofloxacin 400mg IV three times daily OR
  • Imipenem/cilastatin 1g IV three times daily

Consultation

Consult ortho for joint irrigation in OR if joint aspirate is indicative of infection

Disposition

• Admit all to ortho

External Links

• MDCalc - Kocher Criteria for Septic Arthritis

See Also

• Arthrocentesis
• Monoarticular Arthritis
• Septic Arthritis (Hip)
• Septic Arthritis (Peds)
• Knee Diagnoses

Source

• Tintinalli