Septic arthritis is caused by a bacterial infection. The bacteria may enter the joint from a wound, or the bacteria may spread to the joint through the bloodstream from another location in the body. Septic arthritis is more common in those who have a weak immune system.

Causes of septic arthritis include:

• Cellulitis
• Osteomyelitis
• Skin ulcer
• Wound that enters the joint:
• Puncture wound
• Laceration
• Joint surgery
• Arthrocentesis