Infectious arthritis, which is sometimes called septic arthritis or pyogenic arthritis, 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.

Description

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.
* Patients with 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.

Causes and symptoms

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 or a 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 of the 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 develop over 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 hip may 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 fluid into the affected joint. The joint is sore to the touch; it may or may not be warm 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.

Diagnosis

The diagnosis of infectious arthritis depends on a combination of laboratory testing with careful history-taking and physical examination of the affected joint. It is important to keep in mind that 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.

Patient history

The patient's history will tell the doctor whether he or she belongs to a high-risk group for infectious arthritis. Sudden onset of joint pain is also important information.

Physical examination

The doctor will examine the affected joint for swelling, soreness, warmth, and other signs of infection. Location is sometimes a clue to diagnosis; infection of an unusual joint, such as the joints between the breastbone and collarbone, or the pelvic joints, often occurs in drug abusers.

Laboratory tests

Laboratory testing is necessary to confirm the diagnosis of infectious arthritis. The doctor will perform an arthrocentesis, which is a procedure that involves withdrawing a sample of synovial fluid (SF) from the joint with a needle and syringe. SF is a lubricating fluid secreted by tissues surrounding the joints. Patients should be warned that arthrocentesis is a painful procedure. The fluid sample is sent for culture in the sealed syringe. SF from infected joints is usually streaked with pus or looks cloudy and watery. Cell counts usually indicate a high level of white cells; a level higher than 100,000 cells/mm3 or a neutrophil proportion greater than 90% suggests septic arthritis. A Gram's stain of the culture obtained from the SF is usually positive for the specific disease organism.

Doctors sometimes order a biopsy of the synovial tissue near the joint if the fluid sample is negative. Cultures of other body fluids, such as urine, blood, or cervical mucus, may be taken in addition to the SF culture.

Diagnostic imaging

Diagnostic imaging is not helpful in the early stages of infectious arthritis. Destruction of bone or cartilage does not appear on x rays until 10-14 days after the onset of symptoms. Imaging studies are sometimes useful if the infection is in a deep-seated joint.

Treatment

Infectious arthritis requires usually requires several days of treatment in a hospital, with follow-up medication and physical therapy lasting several weeks or months.