Podcast #176 - EM ID: Septic Arthritis

We have Patrick Bafuma back interviewing Dr. Nico Cortes-Penfeld from the University of Nebraska Medical Center.  He specializes in orthopedic infectious diseases.  Nico and Patrick are covering septic arthritis in this conversation.  We include some key pearls in the post but make sure to listen to the podcast for additional information.

Presentation of  symptoms:

• General concepts:
  • Infections should usually involve one joint.
    • If multiple joints have effusions, think rheumatic or ask about travel history (some unique infections like Chikungunya cans cause this).
    • Ghonorrhea, endocarditis, and septic thrombophlebitis can cause multiple joint infections and should be considered when these do present.
  • At least half of cases of septic arthritis involve the knees.
    • In IV drug use (IVDU), they can have some unique joint space infections such as the sternoclavicular or sternomanubrial joints (due to the venous blood supply).
    • Some symptoms can be challenging such as chest pain with the above concerns in IVDU.
  • Common signs and symptoms may not always be impressive.
    • The most common complaint is simply pain and can be isolated.
    • There are your classic findings of calor, dolor, rubor, and tumor (heat, pain, redness, and swelling), but they are not specific.
    • Systemic symptoms are often not seen in elderly patients compared to younger patients.
    • Length of duration of symptoms is not very helpful.
  • Labs can be beneficial but a needle in the joint (arthrocentesis) is most helpful.
    • Labs are best for borderline or indeterminate cases where there is diagnostic uncertainty.
    • Labs from the arthrocentesis: cell count with differential, microscopy for crystals, Gram stain, and a culture (bonus: Nico says if you have lots of fluid put some of that in a blood culture bottle as this can have a better microbiologic yield).
      • Leukocyte count in a synovial fluid collection is more helpful the higher it is.
      • Any WBCs in a prosthetic joint should have us concerned since it is avascular.
      • 80% of the time cultures should yield something.
  • Bacteria are usually Gram positives particularly staph and strep.
    • Oral antibiotics have been demonstrated to be non-inferior in management of septic arthritis compared to IV antibiotics.
    • However, Nico recommends a variety of options which he lists toward the end of the podcast.
• Prosthetic joint infections:
  • A common symptom for infection  is joint instability
    • This can be falls or feeling like their leg is about to give out.
    • The symptom is from the bacteria damaging and loosening the hardware.
  • Systemic symptoms are often missing.
  • Wait for arthrocentesis in these cases if possible given the risk of introducing infection.
  • Infections involving arthroplasty usually requires months of antibiotics and surgeries.
  • Cell counts need to be interpreted differently in prosthetic joints because they are not vascularized.
• Unique situations and tips:
  • Shoulder infections tend to be caused more by Cutibacterium acnes (formerly P. acnes).
  • Septic arthritis in a hand think about bites wounds as this can help with appropriate antibiotics.
  • Septic arthritis after traumatic event, think about other atypical sources such as fungi.
  • Bone and joint infections can occur in areas where previous trauma occurred even years before (such as fractures).
  • Unless systemically ill, try to wait for operative cultures given the benefit of testing this way.

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