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Septic Arthritis

A medical emergency, septic (infectious) arthritis is caused by bacterial invasion of a joint, resulting in inflammation of the synovial lining. If the organisms enter the joint cavity, effusion and pyogenesis follow, with eventual destruction of bone and cartilage.

Septic arthritis can lead to ankylosis and even fatal septicemia. However, prompt antibiotic therapy and joint aspiration or drainage cures most patients.The following types of infectious organisms have been associated with septic arthritis:

• staphylococci (common bacteria that often cause skin infections)
• Haemophilus influenzae (bacteria that can infect the larynx, trachea, and bronchi)
• gram-negative bacilli (a group of bacteria, including Escherichia coli, or E. coli)
• gonococci (bacteria that causes gonorrhea)
• streptococci (a group of bacteria that can lead to a wide variety of diseases)

The most prevalent sites of infection include the following:

• knee
• hip
• ankle
• elbow
• wrist
• shoulder
• pelvis

Most infections affect only one joint.

Causes

Septic arthritis occurs when some type of infecting organism, most often bacteria, reaches a joint. Bacteria can get into a joint through the bloodstream, or through surgery, an injection, or injury that directly contaminates the joint. The cause of septic arthritis in babies and young children is usually staphylococci, hemophilus influenzae, and gram-negative bacilli. In adults and older children, septic arthritis is more commonly caused by gonococci, staphylococci, and streptococci. Mycobacteria, which causes tuberculosis, and the bacteria that causes Lyme disease can also cause septic arthritis. Intravenous drug users and people with diseases that weaken the immune system, such as HIV, are more likely to have septic arthritis caused by gram-negative bacteria. The staphylococcus organism can also be introduced to a joint during arthroscopic surgery and prosthetic joint surgery.

Signs and symptoms

Acute septic arthritis begins abruptly, causing intense pain, inflammation, and swelling of the affected joint, with low­grade fever. It usually affects a single joint. It most often develops in the large joints but can strike any joint, including the spine and small peripheral joints.

CLlNICAL TIP Systemic signs of inflammation may not appear in some patients. Migratory polyarthritis sometimes precedes localization of the infection. If the bacteria invade the hip, pain may occur in the groin, upper thigh , or buttock, or may be referred to the knee.

Diagnosis

The following are common tests used to diagnose septic arthritis:

• Blood culture ;
• Culture of joint fluid or synovial fluid analysis; and
• X-ray of joint(s).

Treatment

Antibiotic therapy

Penicillin G is effective against infections caused by S. aureus, S. pyogenes, S. pneumoniae, S.viridans, and N.gonorrhoeae. A penicillinase-resistant penicillin, such as nafcillin, is recommended for penicillin G-resistant strains of S. aureus; ampicillin, for H. influenzae; gentamicin, for gram-negative bacilli.

Medication selection requires drug sensitivity studies of the infecting organism. Bioassays or bactericidal assays of synovial fluid and bioassays of blood may confirm clearing of the infection.

Other measures

Treatment of septic arthritis requires monitoring of progress through frequent analysis of joint fluid cultures, synovial fluid WBC counts, and glucose determinations.

Codeine or propoxyphene can be given for pain if needed. (Aspirin causes a misleading reduction in swelling, hindering accurate monitoring of progress.) The affected joint can be immobilized with a splint or traction until movement can be tolerated.

Needle aspiration (arthrocentesis) to remove grossly purulent joint fluid should be repeated daily until fluid appears normal. If excessive fluid is aspirated or the WBC count remains elevated, open surgical drainage (usually urthrotomy with lavage of the joint) may he necessary for resistant infection or chronic septic arthritis.

Surgery

Late reconstructive surgery is warranted only for severe joint damage and only after all signs of active infection have disappeared, which usually takes several months. In some cases, the recommended procedure may be arthroplasty or joint fusion.

Prosthetic replacement remains controversial; it may exacerbate the infection. However, it has helped patients with damaged femoral heads or acetabula.

Prevention

Prophylactic (preventive) antibiotics may be helpful for high-risk people.