Septic Arthritis

Septic Arthritis

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 probability algorithm 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.
  • 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.



Nduaguba AM1, Flynn JM, Sankar WN. Septic Arthritis of the Elbow in Children: Clinical Presentation and Microbiological Profile. J Pediatr Orthop. 2015 Jan 8. PMID: 25575360. [PubMed] [Read by QxMD]

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]

Hariharan P1, Kabrhel C. Sensitivity of erythrocyte sedimentation rate and C-reactive protein for the exclusion of septic arthritis in emergency department patients. J Emerg Med. 2011 Apr;40(4):428-31. PMID: 20655163. [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]

Kocher MS1, Zurakowski D, Kasser JR. Differentiating between septic arthritis and transient synovitis of the hip in children: an evidence-based clinical prediction algorithm. J Bone Joint Surg Am. 1999 Dec;81(12):1662-70. PMID: 10608376. [PubMed] [Read by QxMD]


Sean M. Fox
Sean M. Fox
Articles: 583


  1. Sean
    Thanks for doing this. A couple possible mentions on this topic.
    GC classically monoarticular although it occasionally is polyarticular.

    Kocher way over rated. Multiple prospective studies have failed to validate them. MR far better test than us unless just trying to see if there is significant fluid or using to direct needle. 3% pretty high risk for something that can destroy joint in hours to days. I believe most would admit or mri these kids. At min an Ortho consult is indicated.


    • Dr. Cordle,
      Your insight is always appreciated!

      To your points:
      1) Yes, GC does cause monoarticular arthritis… but if you see polyarticular in a sexually active patient, think GC as #1 cause. Actually… if they are sexually active… thinking GC is a righteous plan.
      2) 100% concur that Kocher Criteria are over-rated. If fact, that was part of my point. That being noted, they are often referred to by our consultants and it is, therefore, important for us to know what they actually say. The fact that the original paper argues that having 2 criteria deserves attention is often lost in translation, particularly when everyone wants to focus on the lab values. 2 of those criteria are not lab values… so if the patient has fever and won’t bear weight, then the original paper argued they were at risk. Well, those are the two criteria that often start the conversation in the first place. Thus, it requires our pre-test probability and vigilance to determine whether we should pursue the diagnosis and having “normal” labs should not diminish our concerns.
      3) Also concur that MRI is more sensitive and specific than U/S; however, U/S may help in cases where the diagnosis is still being debated.

      I do think that sometimes we consult Ortho, perhaps, too early… as in calling before giving the child NSAIDs and reassessing. If the kid starts dancing after ibuprofen, then he/she doesn’t likely need the Orthopod.

      Thank you for your continued vigilance!

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