Septic arthritis causes


 * Associate Editor(s)-In-Chief: Jumana Nagarwala, M.D., Senior Staff Physician, Department of Emergency Medicine, Henry Ford Hospital;

Overview
Septic arthritis develops when bacteria or other tiny disease-causing organisms (microorganisms) spread through the bloodstream to a joint. It may also occur when the joint is directly infected with a microorganism from an injury or during surgery. The most common sites for this type of infection are the knee and hip. Most cases of acute septic arthritis are caused by bacteria such as staphylococcus or streptococcus. Chronic septic arthritis (which is less common) is caused by organisms such as Mycobacterium tuberculosis and Candida albicans.

Etiology
Bacteria are carried by the bloodstream from an infectious focus elsewhere, introduced by a skin lesion that penetrates the joint, or by extension from adjacent tissue (e.g. bone or bursae).

Micro-organisms must reach the synovial membrane of a joint. This can happen in any of the following ways:
 * dissemination of pathogens via the blood, from abscesses or wound infections,
 * dissemination from an acute osteomyelitic focus,
 * dissemination from adjacent soft tissue infection,
 * entry via penetrating trauma
 * entry via iatrogenic means.

Bacteria that are commonly found to cause septic arthritis are:
 * Staphylococcus aureus - the most common cause in adults
 * Streptococci - the second most common cause
 * Haemophilus influenzae - was the most common cause in children but is now uncommon in areas where Haemophilus vaccination is practised
 * Neisseria gonorrhoea - in young adults (although this is now thought rare in western europe
 * Escherichia coli - in the elderly, IV drug users and the seriously ill
 * M. tuberculosis, Salmonella spp. and Brucella spp. - cause septic spinal arthritis

In bacterial infection, Pseudomonas aeruginosa has been found to infect joints, especially in children who have sustained a puncture wound. This bacteria also causes endocarditis.