November Week 3: Septic vs. Reactive Arthritis

Article: Arthritis in Children and Adolescents. Peds In Review.


A previously healthy 7-year-old boy presents with a 2-day history of progressive right knee pain and swelling and increasing difficulty bearing weight. He reports falling on the playground 1 week ago but was “fine” after the fall. On physical examination, his temperature is 39.0°C, heart rate is 120 beats/min, and respiratory rate is 25 breaths/min. He is lying on a stretcher, obviously uncomfortable. His right knee is swollen and warm, but there is no significant overlying erythema or effusion. Movement of the knee joint is moderately painful, but he can tolerate the maneuver. His mucous membranes are moist and lungs are clear. His abdomen is benign. There are no other findings of note on the remainder of his examination. His white blood cell count is 25.0×103/mcL (25.0×109/L), with 75% polymorphonuclear leukocytes, 20% lymphocytes, and 5% monocytes. Blood culture results are pending.

Of the following, the MOST likely pathogen causing this patient’s illness is

  • Haemophilus influenza type b
  • Kingella kingae
  • Salmonella non-typhi
  • Staph aureus
  • Strep pyogenes
  • Describe a thorough joint physical exam.
  • Define septic arthritis. Reactive arthritis.
  • At what age range is septic arthritis most commonly seen? Reactive arthritis?
  • What are the most common pathogens responsible for septic arthritis in
  • children? In neonates? In children/teens who have had a history of IV drug use?
  • In children with SCD? In sexually active patients?
  • What are the most common pathogens associated with reactive arthritis?
  • What are the risk factors for septic arthritis in neonates?
  • What is the most common mechanism of infection in septic arthritis?
  • Which joints are most affected in septic arthritis in children? In neonates?
  • What are the presenting symptoms of septic arthritis? Reactive arthritis?
  • In a child with a septic knee, what is the most common position in which they
  • prefer to hold their knee at rest? In a child with a septic hip?
  • T/F. A negative Xray of the affected joint rules out septic arthritis?
  • Which imaging study is the most sensitive in detecting early signs of septic joint?
  • Signs of reactive arthritis?
  • T/F. Arthrocentesis is a mandatory procedure when septic arthritis is suspected?
  • What are some long-term sequelae of untreated or delayed treatment of septic
  • joint?
  • What is the general treatment approach for septic arthritis? Reactive arthritis?