How can bacteria enter a joint and cause septic arthritis?

Bacteria can enter a joint and cause septic arthritis through three primary routes of infection:1

• Bloodstream (Hematogenous): This is the most common pathway. Bacteria enter the circulatory system from an infection elsewhere in the body and reach the joint through the synovial blood vessels.12
• Direct Contamination: Microorganisms are introduced directly into the joint space, typically through penetrating wounds or during surgery.12
• Extension from Adjacent Infection: Bacteria can spread to the joint from nearby bony infections, such as osteomyelitis. The infection moves from the bone into the joint through natural openings or breaches in the bone's outer layer.1

Once inside, these bacteria—such as Staphylococcus, Streptococcus, or Neisseria gonorrhoeae—trigger an inflammatory response. The resulting production of pus can rapidly erode articular cartilages, which have little capacity for regeneration, potentially leading to permanent joint damage if not treated promptly with antimicrobial therapy and drainage.321