Causes

Septic arthritis develops when bacteria spreads from the source of infection through the bloodstream to a joint; it can result from direct infection through an injection, penetration wound, during surgical procedures, or injury that directly contaminates the joint.

It can strike at any age but occurs most often in children younger than age three. In infants, the hip is a frequent site of infection; in toddlers, it’s the shoulders, knees, and hips. In these young patients, the most common bacterial causes are:

• Staphylococci ( “staph” infections)
• Streptococci that trigger “strep” throat
• Streptococcus pneumoniae , the bacterium responsible for most identified cases of pneumonia .

Septic arthritis rarely occurs from early childhood through adolescence. After that, its incidence increases. In adults, it most commonly affects weight-bearing joints such as the knees. Mycobacteria, which causes tuberculosis , and the bacterium that causes Lyme disease , can also result in septic arthritis.

Joint Damage in Knee

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Risk Factors

The following factors increase your chances of developing septic arthritis. If you have any of these risk factors, tell your doctor:

• Diseases that weaken the immune system, such as HIV , or taking drugs that suppress immunity.
• A history of joint problems or having other types of arthritis , gout , or lupus .
• A history of intravenous drug use.
• Chronic illnesses such as anemia , diabetes , sickle cell , or kidney failure.
• Having joint replacement or organ transplant surgery.
• Skin conditions such as psoriasis or eczema that could allow for infections to penetrate through the skin.