Acute inflammation of one or more joints caused by infection. Suppurative arthritis may follow certain bacterial infections; joints become swollen, hot, sore, and filled with pus, which erodes their cartilage, causing permanent damage if not promptly treated by giving antibiotics, draining the pus, and resting the joint. Nonsuppurative arthritis can accompany several diseases caused by bacteria, viruses, or fungi; joints become stiff, swollen, and painful to move. Treatment includes rest, drugs, and, in the case of tuberculosis, orthopedic care to prevent skeletal deformity.

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Septic arthritis is the invasion of a joint by an infectious agent which produces arthritis. The usual etiology is bacterial, but viral, mycobacterial, and fungal arthritis occur occasionally. 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).

Etiology

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
• Haemophilus influenzae - the most common cause in children
• Neisseria gonorrhoea - in young adults
• 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.

Indications

Septic arthritis should be suspected when one joint (monoarthritis) is affected and the patient is febrile. In seeding arthritis, several joints can be affected simultaneously; this is especially the case when the infection is caused by staphylococcus or gonococcus bacteria.

Diagnosis is by aspiration (giving a turbid, non-viscous fluid), Gram stain and culture of fluid from the joint, as well as tell-tale signs in laboratory testing (such as a highly elevated neutrophils (approx. 90%), ESR or CRP).

Treatment

Therapy is usually with intravenous antibiotics, analgesia and washout/aspiration of the joint to dryness.

Radiologic Findings

Traditionally, the diagnosis of septic arthritis was based on clinical assessment and prompt arthrocentesis. However, the clinical picture may be obscured by multiple confounding factors and a paucity of specific findings especially for the deep joints, ie. the hip or shoulder. Imaging can be used to confirm the diagnosis of septic arthritis and more importantly, imaging findings suggestive of septic arthritis can direct the clinician to a diagnosis that may not have been considered.

Plain film findings of septic arthritis include: joint effusion, soft tissue swelling, periarticular osteoporosis, loss of joint space, marginal and central erosions and bone ankylosis. CT is more sensitive than plain films for the detection of early bone destruction and effusion.

The role of MRI in the diagnosis of septic arthritis has been increasing in recent years in an effort to detect this entity earlier. Findings are usually evident within 24 hours following the onset of infection and include: synovial enhancement, perisynovial edema and joint effusion. Signal abnormalities in the bone marrow can indicate a concomitant osteomyelitis. The sensitivity and specificity of MRI for the detection of septic arthritis has been reported to be 100% and 77% respectively.

See also

• Arthritis
• Human biting injuries
• Transient synovitis
• Arthritis Care

References

• Septic arthritis by William Brinkman, M.D., University of Washington Department of Radiology
• Karchevsky M, Schweitzer ME, Morrison WB, Parellada JA (2004). "MRI findings of septic arthritis and associated osteomyelitis in adults". AJR Am J Roentgenol 182 (1): 119–22.
• Resnick, Donald (1989). Bone and joint imaging. Philadelphia: Saunders.
• Bredella, Miriam A.; Stoller, David W.; Tirman, Phillip F. J. (2004). Diagnostic imaging. Salt Lake City, Utah: Amirsys.
• Edwards MS. "Osteomyelitis and Septic Arthritis"