Septic Arthritis

Originally published at Pediatric EM Morsels on August 28, 2015. Reposted with permission.

Follow Dr. Sean M. Fox on twitter @PedEMMorsels

We have discussed several entities that may lead to a child limping. We have covered osteomyelitis, plantar punctures, and toddler’s fractures.  We have also touched upon Osgood Schlatter’s Disease, SCFE, osteosarcoma and even Growing Pains. Now let us review a topic that always crosses our minds when considering the painful extremity: Septic Arthritis.

Septic Arthritis: Basics

  • Septic arthritis is an infection in the joint space and synovial fluid.
  • Can occur by hematogenous spread of bacteria or direct inoculation.
  • High Risk populations = children less than 2 years of age, immunocompromised, and patients without functional spleens
  • Complications:
    • Capsule damage
    • Chronic arthritis
    • Osteonecrosis
    • Growth Arrest
    • Sepsis

Septic Arthritis: Presentation

  • Fever
    • Although no/low fever noted in up to 20% of cases!
  • Joint pain, swelling, and erythema
    • Pain with passive range of motion!
    • Limps or refuses to bear weight on limb.
  • 80% of cases in children involve the lower limbs
    • Knee involved in 40% of cases
    • Hip involved in 20% of cases

Septic Arthritis: The Bugs

  • Staph aureus = most common organism across all ages
    • MRSA has become more prevalent [Young, 2011]
    • Group B Strep is 2nd most common
  • Special Population considerations:
    • Infants:
      • E. Coli
    • Young Children (<4 years)
      • Klingella kingae (notoriously difficult to culture)
      • Hemophilus influenza B has become less prevalent since HiB vaccination.
    • Immunocompromised:
      • Klingella kingae
      • Streptococcus pneumoniae (especially with HIV infection)
    • Sickle Cell Disease:
      • Salmonella (although, S. Aureus is still most common)
    • Sexually Active:
      • N. Gonorrhea – most common cause of polyarticular infections in sexually active patients

Septic Arthritis vs. Toxic Synovitis

  • Despite the name, toxic synovitis is the self-limited, benign inflammation of the joint that gets treated symptomatically.
  • Unfortunately, the presentation of toxic synovitis can be difficult to differentiate from septic arthritis, particularly when involving the hip joint.
    • Atraumatic 
    • Acute pain
    • Limp / refuses to bear weight
    • Fever
  • The treatment strategies and potential outcomes are quite different for the two conditions, so differentiating between them is critical… although challenging. (again, your job isn’t easy)

Septic Arthritis: Kocher’s Criteria

  • In 1999, Kocher et al published retrospective data from cases that presented to their facility from 1979-1996 due to “acutely irritable hip.”
  • Through a logistic regression analysis of 168 patients, they devised a probabilityalgorithm to help differentiate between septic arthritis and toxic synovitis.
  • There was no single lab test that was able to differentiate between the two entities. [Kocher, 1999]
  • Kocher’s Criteria: [Kocher, 1999]

    • Predictors associated with risk of Septic Arthritis
      • Fever
      • Non-weight-bearing
      • ESR = 40 or more
      • Serum WBC = 12,000 or more
    • Probability of Septic Arthritis based on number of Predictors
      • 0 Predictors – <0.2 %
      • 1 Predictor – 3.0%
      • 2 Predictors – 40.0%
      • 3 Predictors – 93.1%
      • 4 Predictors – 99.6%
  • Use this information wisely… not blindly.
    • May not apply to your patient.
      • Not hip pain?
      • Any underlying high-risk factors?
      • Clinical Decision Rules typically have diminished performance in different populations other than the derivation group. [Kocher, 2004]
    • Must balance the risk of false-positives vs false-negatives.
      • At what point does risk of missing septic arthritis outweigh the morbidity of joint aspiration? [Kocher, 1999].
        • 0 or 1 Predictors – close follow-up / observation
        • 2 Predictors – Aspiration via fluoroscopy/ultrasound
        • 3 or 4 Predictors – Aspiration in OR with likely arthrotomy and drainage.

Morals of the Morsel

  • Septic Arthritis needs to be higher on your differential than Toxic Synovitis.
  • Appreciate the diagnostic challenge inherent in the evaluation.
  • NO SINGLE TEST WILL DIAGNOSE OR RULE-OUT SEPTIC ARTHRITIS. [Dodwell, 2013]
  • Anticipate what tool (ex, Kocher Criteria) your consultants will likely use, but know their limitations.
  • 2 Predictors is more reassuring than 3, but still comes with increased risk.
    • Having Fever and being Non-Weight Bearing with normal labs can still be associated with Septic Arthritis!
  • Your pretest probability has to be taken into account, like always.
  • Don’t forget to give some analgesics!  
    • The child who is now weight-bearing after NSAIDs just became less concerning and it may be better to arrange close followed-up rather than ordering a bunch of non-specific lab tests.

References

Montgomery NI1, Rosenfeld S. Pediatric osteoarticular infection update. J Pediatr Orthop. 2015 Jan;35(1):74-81. PMID: 24978126. [PubMed] [Read by QxMD]

Dodwell ER1. Osteomyelitis and septic arthritis in children: current concepts. Curr Opin Pediatr. 2013 Feb;25(1):58-63. PMID: 23283291. [PubMed] [Read by QxMD]

Gill KG1. Pediatric hip: pearls and pitfalls. Semin Musculoskelet Radiol. 2013 Jul;17(3):328-38. PMID: 23787987. [PubMed] [Read by QxMD]

Young TP1, Maas L, Thorp AW, Brown L. Etiology of septic arthritis in children: an update for the new millennium. Am J Emerg Med. 2011 Oct;29(8):899-902. PMID:20674219. [PubMed] [Read by QxMD]

Yuan HC1, Wu KG, Chen CJ, Tang RB, Hwang BT. Characteristics and outcome of septic arthritis in children. J Microbiol Immunol Infect. 2006 Aug;39(4):342-7. PMID:16926982. [PubMed] [Read by QxMD]

Kocher MS1, Mandiga R, Zurakowski D, Barnewolt C, Kasser JR. Validation of a clinical prediction rule for the differentiation between septic arthritis and transient synovitis of the hip in children. J Bone Joint Surg Am. 2004 Aug;86-A(8):1629-35. PMID: 15292409.[PubMed] [Read by QxMD]

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