What is the role of imaging in the diagnosis of septic arthritis?

Updated: Sep 19, 2019
  • Author: Lourdes Nunez-Atahualpa, MD; Chief Editor: Felix S Chew, MD, MBA, MEd  more...
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Imaging is not the primary means of diagnosing septic arthritis. Clinical evaluation and joint fluid aspiration are the key to the diagnosis. [5] Samples should be obtained in all suspected cases of septic arthritis. This sampling can usually be achieved with fine-needle aspiration performed either blindly or guided though imaging methods, such as fluoroscopy, ultrasound, MRI, or CT, depending on the location. Surgical exploration may be necessary.

Fluid should be sent for Gram staining, culturing, glucose testing, leukocyte count, and differential determination. White blood cell counts are usually 50,000-60,000/µL, with more than 80% neutrophils. Synovial fluid glucose levels are decreased. Gram stain results are positive in 75% of patients with gram-positive cocci. Gram staining is less sensitive in cases of gonococcal infection. Only 25% of cultures of gonococcal synovial fluid are positive. In 9% of cases, blood cultures are the only source of pathogen identification and should be obtained before antibiotic treatment. [23]

Multiple imaging modalities are available for assessing septic arthritis. Plain radiography and ultrasound have been suggested to be the preferred initial study. [9]  However, if further imaging is required, MRI is the most sensitive and specific technique. Scintigraphy, CT, and FDG-PET are also used, although to a lesser extent. [8, 17, 18, 9, 19, 20, 21, 22]

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