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
• Gonococcal arthritis is the most common cause in adolescents and young adults

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

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

Treatment

1. Joint drainage
2. Abx
   1. Gram stain can be used to guide treatment
      1. Gram+: vancomycin IV
      2. Gram- OR gonococcus suspected: Ceftriaxone IV 2gm daily
3. 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
• Sensitivity of Erythrocyte Sedimentation Rate and C-reactive Protein for the Exclusion of Septic Arthritis in Emergency Department Patients http://dx.doi.org/10.1016/j.jemermed.2010.05.029