Infectious arthritis

Infectious arthritis, which is sometimes called septic arthritis or pyogenicarthritis, is a serious infection of the joints characterized by pain, fever, occasional chills, inflammation and swelling in one or more joints, and loss of function in the affected joints. It is considered a medical emergency.

Infectious arthritis can occur in any age group, including newborns and children. In adults, it usually affects the wrists or one of the patient's weight-bearing joints--most often the knee--although about 20% of adult patients have symptoms in more than one joint. Multiple joint infection is common in children and typically involves the shoulders, knees, and hips.

Some groups of patients are at greater risk for developing infectious arthritis. These high-risk groups include:

  • Patients with chronic rheumatoid arthritis.
  • Patients with certain systemic infections, including gonorrhea and HIV infection. Women and male homosexuals are at greater risk for gonorrheal arthritis than are male heterosexuals.
  • Patients with certain types of cancer.
  • IV drug abusers and alcoholics.
  • Patients with artificial (prosthetic) joints.
  • Patientswith diabetes, sickle cell anemia, or systemic lupus erythematosus (SLE).
  • Patients with recent joint injuries or surgery, or patients receiving medications injected directly into a joint.

In general, infectious arthritis is caused by the spread of a bacterial, viral, or fungal infection through the bloodstream to the joint. The disease agents may enter the joint directly from the outside as a result of an injury ora surgical procedure, or they may be carried to the joint by the blood from infections elsewhere in the body. The specific organisms vary somewhat according to age group. Newborns are most likely to acquire gonococcal infections ofthe joints from a mother with gonorrhea. Children may also acquire infectious arthritis from a hospital environment, often as a result of catheter placement. The organisms involved are usually either Haemophilus influenzae (in children under two years of age) or Staphylococcus aureus. In older children or adults, the infectious organisms include Streptococcus pyogenes and Streptococcus viridans as well as Staphylococcus aureus. Staphylococcus epidermidis is usually involved in joint infections related to surgery. Sexually active teenagers and adults frequently develop infectious arthritis from Neisseria gonorrhoeae infections. Older adults are often vulnerable to joint infections caused by gram-negative bacilli, including Salmonella and Pseudomonas.

Infectious arthritis often has a sudden onset, but symptoms sometimes developover a period of three to 14 days. The symptoms include swelling in the infected joint and pain when the joint is moved. Infectious arthritis in the hipmay be experienced as pain in the groin area that becomes much worse if the patient tries to walk. In 90% of cases, there is some leakage of tissue fluidinto the affected joint. The joint is sore to the touch; it may or may not bewarm to the touch, depending on how deep the infection lies within the joint. In most cases the patient will have fever and chills, although the fever may be only low-grade. Children sometimes develop nausea and vomiting.

Septic arthritis is considered a medical emergency because of the damage it causes to bone as well as cartilage, and its potential for creating septic shock, which is a potentially fatal condition. Staphylococcus aureus is capable of destroying cartilage in one or two days. Destruction of cartilage and bone in turn leads to dislocations of the joints and bones. If the infection is caused by bacteria, it can spread to the blood and surrounding tissues,causing abscesses or even blood poisoning. The most common complication of infectious arthritis is osteoarthritis.

The diagnosis of infectious arthritis depends on a combination of laboratorytesting with careful history-taking and physical examination of the affectedjoint. Infectious arthritis can coexist with other forms of arthritis, gout, rheumatic fever, Lyme disease, or other disorders that can cause a combination of joint pain and fever. In some cases, the doctor may consult a specialist in orthopedics or rheumatology to avoid misdiagnosis.

Infectious arthritis requires usually requires several days of treatment in ahospital, with follow-up medication and physical therapy lasting several weeks or months. Because of the possibility of serious damage to the joint or other complications if treatment is delayed, the patient will be started on intravenous antibiotics before the specific organism is identified. Afterthe disease organism has been identified, the doctor may give the patient adrug that targets the specific bacterium or virus. Nonsteroidal anti-inflammatory drugs are usually given for viral infections. Intravenous antibiotics are given for about two weeks, or until the inflammation has disappeared. The patient may then be given a two- to four-week course of oral antibiotics.

In some cases, surgery is necessary to drain fluid from the infected joint.

Patients with severe damage to bone or cartilage may need reconstructive surgery, but it cannot be performed until the infection is completely gone.

Infectious arthritis requires careful monitoring while the patient is in thehospital. The doctor will drain the joint on a daily basis and remove a smallsample of fluid for culture to check the patient's response to the antibiotic.

About 70% of patients will recover without permanent joint damage. However, many patients will develop osteoarthritis or deformed joints. Children with infected hip joints sometimes suffer damage to the growth plate of the bone. Iftreatment is delayed, infectious arthritis has a mortality rate between 5% and 30% due to septic shock and respiratory failure.

Some cases of infectious arthritis are preventable by lifestyle choices. These include avoidance of self-injected drugs; sexual abstinence or monogamous relationships; and prompt testing and treatment for suspected cases ofgonorrhea.

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