Septic arthritis resident survival guide

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Septic arthritis
Resident Survival Guide

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Iqra Qamar M.D.[2], Aditya Ganti M.B.B.S. [3]



Gram-negative bacilli account for 10 to 20% of septic arthritis causes.[1] ~10% of patients with nongonococcal septic arthritis are due to polymicrobial cause of infections. Anaerobes are also can cause septic arthritis in few cases. Most common cause of septic arthritis in children age < 2 years are Haemophilus influenzae (in immunized children), Staph. aureus, group A Streptococcal infections and Kingella kingae.[2] The source of infection in most of the cases (~50%) often from the skin, lungs or bladder.

Common Causes

Common microorganisms causing septic arthritis includes:[3][4][5][3][6][3][7]

Less Common Causes



Complete diagnostic approach:

Common Presentation

Symptoms in newborns or infants:

  • Cries when infected joint is moved (e.g. diaper change causes crying if hip joint is infected)
  • Fever
  • Inability to move the limb with the infected joint (pseudoparalysis)
  • Irritability

Symptoms in children and adults:

Less common Presentation


Focused History

  • Intravenous drug use
  • Sexual activity
  • Terminal complement deficiency
  • Dog or cat bite
  • Ingestion of unpasteurized dairy products
  • Nail through shoe
  • Soil exposure/gardening
  • Soil or dust exposure containing decomposed wood

(north-central and southern United States)

  • Southwestern United States, Central and South America

(primary respiratory illness)

  • Cleaning fish tank

Physical Examination

Appearance of the Patient

Vital Signs


  • Warmth over the joint


Most commonly involves knee > hip > shoulder > ankle.[9] Other joints such as sacroiliac joint (~10%), sternoclavicular or costoclavicular joints may be involved in patient with history of intravenous drug abuse (IVDA), penetrating trauma, animal or human bites and local steroid injections.

  • Swelling of the joint that involved
  • Decreased range of motion such as pseudo paralysis
  • Patient hold the hip in flexed and externally rotated position if SA involving hip.
  • If child, unwillingness to bear weight on the affected joint (antalgic gait)

Laboratory Workup


Imaging Study

Plain radiographs of swollen joints

  • Swelling of the joint capsule and soft tissue around the joint
  • Fat pad displacement
  • Joint space widening due to localized edema and effusion.[10][11][12]

Computed tomography (CT)

  • Visualization of joint effusion
  • Soft tissue swelling
  • Para-articular abscesses
  • Joint space widening due to localized edema, bone erosions, foci of osteitis, and scleroses.[13][11]

Magnetic resonance imaging (MRI)

  • Synovial enhancement
  • Perisynovial edema
  • Joint effusion
  • Signal abnormalities in the bone marrow

Other Investigation



  • In the presence of joint effusion to differentiate between different causes of arthritis[14]

Synovial Fluid Analysis

Synovial fluid analysis include:[8]

  • Synovial WBC count with differential
  • Crystal analysis
  • Gram stain
  • Culture and sensitivity

Normal synovial fluid appears as clear, transparent, thick in viscosity with WBC count less than 200 mm3 and < 25% of PMN, where as in septic arthritis and other arthritis synovial fluid analysis will be as follows:[15][16][17][18][19][20][21][22]

Type of


Color Transparency Viscosity WBC count

(per mm3)


cellcount (%)

Gram stain Gram Culture polymerase chain reaction

(PCR) test

Normal Clear Transparent High/thick < 200 < 25 Negative Negative Negative Negative
Gonococcal arthritis Yellow Cloudy-opaque Low 34,000 to 68,000 > 75 Variable (< 50 percent) Positive (25 to 70 percent) Positive (> 75 percent) Negative
Non-gonococcal arthritis Yellowish-green Opaque Very low > 50,000 (> 100,000 is

more specific)

> 75 Positive (60 to

80 percent)

Positive (> 90 percent) -- Negative

crystalline arthritis

(e.g.Gout, Pseudogout)

Yellow Cloudy Low/thin 2,000 to 100,000 > 50 Negative Negative Negative Positive

non-crystalline arthritis

(e.g. Rheumatoid arthritis, reactive arthritis)

Yellow Cloudy Low/thin 2,000 to 100,000 > 50 Negative Negative Negative Negative
Noninflammatory arthritis

(e.g. Osteoarthritis)

Straw Translucent High/thick 200 to 2,000 < 25 Negative Negative Negative Negative
Lyme's arthritis Yellow Cloudy Low 3,000 to 100,000

(mean: 25,000)

> 50 Negative Negative Positive (85 percent) Negative


Empiric treatment should be commenced as soon as possible after culture samples have been obtained. The choice of empiric antibiotics should be determined on the basis of:[11][23][24]

If the patient fails to respond to initial treatment, consider:[11]

  • Misidentification of causative pathogen
  • Infection with atypical pathogen
  • Concurrent osteomyelitis
  • Occult nidus of infection

Intra-articular antibiotics are not useful as it may increase infection rate and also causes chemical synovitis and cartilage toxicity.[25]

Methicillin-resistant Staphylococcus aureus (MRSA)

Patient at high risk of methicillin-resistant Staphylococcus aureus (MRSA) include:[26][27]

  • Known MRSA colonization or infection
  • Recent hospitalization
  • Nursing-home resident
  • Presence of leg ulcers
  • Indwelling catheters

Antimicrobial Regimen – Empiric Therapy:

Newborn (< 1 week) Newborn (1–4 weeks) Infants (1–3 months) Children (3 months–14 years) Adults

High Risk for MRSA

Low Risk for MRSA

High Risk for MRSA

Low Risk for MRSA

High Risk for MRSA

Low Risk for MRSA

Preferred Regimen



Antimicrobial Regimen – Synovial Fluid Gram Stain-Based Therapy:

Gram stain result First choice antibiotic Second choice antibiotic
Negative Gram stain


Gram-positive cocci
Gram-negative cocci
Gram-negative bacilli

Antimicrobial Regimen – Pathogen Based Therapy:

Microorgnaism First choice antibiotic Second choice antibiotic
Staphylococcus aureus Methicillin-sensitive
  • Vancomycin 15–20 mg/kg IV q8–12h in adults or 15 mg/kg IV q6h in children or
  • Linezolid 600 mg PO/IV q12h in adults or 10 mg/kg PO/IV q8h in children
Coagulase-negative Staphylococcus spp Methicillin-sensitive
Group A streptococcus, Strep. pyogenes
Group B streptococcus, Strep. agalactiae
Enterococcus spp.
Escherichia coli
Proteus mirabilis
Proteus vulgaris, Proteus rettgeri, Morganella morganii
Serratia marcescens
Pseudomonas aeruginosa
Neisseria gonorrhea
Bacteroides fragilis group
Brucella melitensis
Haemophilus influenzae
Morganella morganii
Tropheryma whipplei
Borrelia burgdorferi

Duration of Antimicrobial Therapy:

Clinical Setting Duration
Staphylococcus aureus infection 3–4 weeks
Streptococcus groups A, B, C, G infection 3–4 weeks
Gram-negative bacilli infection 4 weeks
Brucella infection 6 weeks
Borrelia burgdorferi infection 30 days
Mycobacterium tuberculosis infection 9 months
Candida albicans infection 6 weeks
Prosthetic joint infection 6 weeks
Post-intraarticular injection or post-arthroscopy 14 days




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