What is septic arthritis (SA)?

Updated: Sep 19, 2019
  • Author: Lourdes Nunez-Atahualpa, MD; Chief Editor: Felix S Chew, MD, MBA, MEd  more...
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Septic arthritis (SA) in the United States has an annual incidence of 10 per 100,000. [1]  It is more prevalent in patients who are elderly (80 years or older), have prosthetic joints, have undergone joint surgery, have immunocompromised states such as HIV, have skin infections, or have autoimmune diseases. [2, 3]  In general, infectious arthritis is classified as pyogenic (septic) or nonpyogenic. Pyogenic septic arthritis is caused by Staphylococcus aureus in up to 80% of cases, [5, 6]  followed by other pathogens such as staphylococci, streptococci, Gonococcus species, Escherichia coli, Haemophilus, Klebsiella, Pseudomonas, and Candida. Infection can lead to rapid and severe joint destruction. Nonpyogenic infective arthritis tends to be less aggressive and have a more chronic course, with causative organisms including Mycobacterium tuberculosis, fungi, and spirochetes. [8, 2, 3]

Septic arthritis can be acquired through several routes of transmission. The most common cause is acquisition through hematogenous spread from a distant source. Direct seeding can occur through trauma, surgery, or spread from a contiguous infection such as osteomyelitis or cellulitis.

Septic arthritis images are provided below.

A 30-year-old man who was taking steroids presente A 30-year-old man who was taking steroids presented with a joint effusion and knee pain. Anteroposterior view of the knee demonstrates patchy demineralization of the tibia and femur and joint-space narrowing. This was caused by tuberculoid infection of the joint.
Coronal short-tau inversion recovery MRI of the pu Coronal short-tau inversion recovery MRI of the pubic symphysis demonstrates a hyperintense joint effusion and increased signal intensity in the bone marrow of the pubic rami. Abnormal high signal intensity is also present in the bilateral hip adductor muscles. The diagnosis was septic arthritis with associated osteomyelitis and inflammatory changes in the soft tissues.
Septic arthritis. Anteroposterior view of the shou Septic arthritis. Anteroposterior view of the shoulder demonstrates subchondral erosions and sclerosis in the humeral head. These are relatively late findings of septic arthritis. Periosteal reaction due to coincident osteomyelitis is present adjacent to the surgical neck of the humerus.
Coronal T2-weighted fat-saturated MRI of the shoul Coronal T2-weighted fat-saturated MRI of the shoulder demonstrates a joint effusion, bone marrow edema, and marked adjacent soft tissue inflammation with a fluid collection in the infraspinatus muscle. This is an example of septic arthritis with associated soft tissue abscess.

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