3. SUMMARY
Septic (infectious) arthritis is a bacterial infection of the joint space.
Contamination occurs either via the bloodstream, iatrogenically, or
by local extension (e.g., penetrating trauma) and patients with
damaged (e.g., patients with rheumatoid arthritis) or
prosthetic joints have an increased risk. Patients usually present with
an acutely swollen, painful joint, limited range of motion, and
a fever. Suspected infectious arthritis requires
prompt arthrocentesis for diagnosis. In addition to the
immediate broad-spectrum antibiotic therapy, surgical drainage
and debridement may be necessary to prevent cartilage destruction
and sepsis.
4. ETIOLOGY
Mechanism of infection
Hematogenous spread (most common)
From a distant site (e.g., abscesses, wound infection, septicemia)
Direct contamination
Trauma (e.g., open wounds around the joint, penetrating trauma)
Risk factors
Prosthetic implant
Interventions
Immunosuppressed state
Diabetes mellitus
Age > 80 years
IV drug use
Causative organisms
Staphylococcus aureus - most common, in adults and children > 2 years
Streptococci
N. gonorrhea
Gram-negative rods esp. E. coliand P. aeruginosa
5. CLINICAL FEATURES
Acute onset Joint involvement
Usually monoarticular
Most commonly
affected joints: knees
Classical triad
of fever, joint pain, and
restricted range of motion
Joint may be swollen, red,
and warm
6. SUBTYPES AND
VARIANTS
Prosthetic joint infection
Etiology [4]
Early onset (< 3 months of placement); most commonly S. aureus
Delayed onset (3–12 months of placement); particularly S. epidermidis
most commonly S. aureus
Clinical findings
Usually prolonged, low-grade course
Can present acutely
7. Bacterial coxitis (septic arthritis of the hip)
Bacterial coxitis is an orthopedic emergency!
Gonococcal arthritis
See purulent gonococcal arthritis and arthritis-dermatitis
syndrome.
Gonococcal arthritis is the most common form of arthritis
in sexually active young adults! In a young, sexually active
adult presenting with classic symptoms
of septic arthritis, gonococcal infection must be ruled out!
Lyme disease
See Lyme arthritis.
8. DIAGNOSTICS
If septic arthritis is suspected, arthrocentesis should be
conducted for synovial fluid analysis.
Ultrasound-guided arthrocentesis: Definitive diagnosis requires
detection of bacteria in the synovial fluid.
To conduct synovial fluid analysis, gram stain, and culture
↑ Synovial fluid WBC and dominance of polymorphonuclear (PMN) cells
Cell count: > 50,000 WBC/μl (neutrophil predominant) points
to septic arthritis (can be as low as > 10,000 in early disease).
9.
10.
11.
12.
13.
14. Appearance
WBCs/μl (PMN %) Glucose levels Culture Crystals
Normal synovial
fluid
•Transparent
•Clear and viscous
•< 200 (< 25%) •Nearly equal
to blood
•Negative •None
Noninflammatory
arthritis
•Transparent
•Yellow and viscous
•200–2000 (< •Nearly equal
to blood
•Negative •Calcium phosphate crystals (apatite): ∼
60% of osteoarthritis cases
Inflammatory •Translucent-opaque
•Yellow and watery
•> 2,000 (≥ 50%) •Lower than
blood
•Negative •Monosodium urate crystals: gout
•Calcium pyrophosphate crystals: pseudogo
Septic •Opaque
•Yellow or green with
variable viscosity
•> 50,000 (≥ 75%)
•Early: > 10,000 (≥
75%)
•Much lower
than blood
•Usually
positive
•None
Hemorrhagic •Cloudy
•Reddish with variable
viscosity
•200–2,000 (50%–
75%)
•Nearly equal
to blood
•Negative •None
DIFFERENTIAL DIAGNOSIS BASED ON SYNOVIAL FLUID
ANALYSIS FINDINGS
15. FURTHER
DIFFERENTIAL
DIAGNOSES TO
CONSIDER
Viral arthritis
Etiology: parvovirus B19, hepatitis B virus, hepatitis C virus, rubella
virus, HIV
Clinical findings
Symmetric involvement of multiple small joints
Sudden onset
Non-infectious arthritis
Acute onset, monoarticular arthritis
Gout
Pseudogout
Reactive arthritis
Joint trauma
Acute or sub-acute onset polyarthritis
differential diagnoses of inflammatory arthritis
The differential diagnoses listed here are not exhaustive.
16. TREATMENT
Initial management
simultaneous empiric antibiotic therapy (based on the Gram
stain) and evacuation of purulent material
Empiric antibiotic regimens
Gram-negative bacilli: 3rd generation
cephalosporin (e.g., ceftazidime), cefepime
serial drainage with lavage
Sometimes debridement
17. FURTHER
MANAGEMENT
Organism Antibiotics
S. aureus and other gram-
positive cocci
•Penicillinase-resistant penicillines
• Oxacillin, nafcillin
• Cefazolin
• MRSA: Vancomycin
Gram-negative cocci •Aminoglycosides
•Ceftriaxone
Gram-negative rods •Ceftazidime, cefepime
N. gonorrhea •IV ceftriaxone
Chlamydia •Doxycycline
Treatment of adults after culture has returned
Treatment of children
•> 3 months: nafcillin + cefazolin