Septic arthritis is primarily caused by what process?

• A. Bacteria in the joint causing inflammation; can spread from blood or open injury; needs to go to the OR.
• B. Autoimmune mediated synovitis.
• C. Viral infection of the joint.
• D. Degenerative wear and tear.

Answer: (C)

Septic arthritis is an infection of the joint space by bacteria that triggers a rapid, purulent inflammatory reaction in the synovium. Bacteria reach the joint either through the bloodstream (hematogenous spread) or by direct inoculation from an open wound or penetrating injury. Because the infection can destroy cartilage and joint structures quickly, it’s a medical emergency.

The best description is a bacterial invasion of the joint causing inflammation with purulent effusion, often needing joint drainage and antibiotics. In adults, Staphylococcus aureus is the most common culprit; Neisseria gonorrhoeae is also seen in certain populations. Management starts with urgent joint aspiration for culture and Gram stain, followed by empiric IV antibiotics after cultures are obtained, with surgical drainage or debridement if purulence is present or if there’s no rapid improvement.

Viral arthritis and autoimmune synovitis are not septic processes. Viral arthritis can occur after infections but septic arthritis specifically implies a bacterial infection of the joint. Degenerative wear and tear (osteoarthritis) is a noninflammatory degenerative process, not an infection.