What Is Septic Arthritis?
Infectious
arthritis is a general term used to describe forms of arthritis that are caused by germs, such as bacteria or viruses. There are several different types of infectious arthritis. One of these types is septic arthritis, or arthritis caused by bacteria
(see Infectious Arthritis to learn about other forms of infectious arthritis).
Septic arthritis is considered a medical emergency because without prompt treatment, the condition can cause permanent damage to the joints involved. It can also cause septic shock, which is a potentially fatal condition.
Septic arthritis is also known as:
Anyone can get septic arthritis. However, most cases of septic arthritis involve infants or children younger than the age of three. Infants are most likely to develop this condition in the hip; children are most likely to develop it in the knee.
Septic arthritis has been estimated to occur in up to 10 people per 100,000 in the general population and in as many as 70 people per 100,000 in people with
rheumatoid arthritis.
What Causes Septic Arthritis?
The cause of this condition is a bacterial infection within a joint or joints (90 percent of such infections affect only one joint). These bacteria cause inflammation within the joint that can ultimately lead to damage to the cartilage (the slippery coating at the end of bones), underlying bone, and joint capsule.
There are several different types of bacteria that are known to cause septic
arthritis. Among infants under one year of age, the most common cause of septic arthritis is
Staphylococcus aureus or Group B Strep. In cases involving adults, the most common cause of septic arthritis is an infection with
Neisseria gonorrhoeae (the bacteria that cause
gonorrhea).
A risk factor is anything that increases a person's chances of developing a disease. Having risk factors for septic arthritis does not guarantee that a person will develop the condition; it just increases his or her chances of developing it.
Some risk factors for septic arthritis include:
- Age (infants and young children are at greatest risk for septic arthritis)
- Infection in another part of the body, especially infection within bone (known as osteomyelitis)
- Alcoholism or IV drug abuse
- Immunosuppressive medicines
- Rheumatoid arthritis, gout, or osteoarthritis
- Previous joint damage
- A history of recent steroid injections into the joint
- Having recently undergone certain surgical procedures (such as a knee replacement, hip replacement, or knee arthroscopy).
Symptoms of Septic Arthritis
Septic
arthritis symptoms (along with their severity) can vary depending on a number of factors, including:
- The age of the person
- The joint or joints involved
- The type of bacteria causing the condition
- Other conditions the person may have.
Specific symptoms may include:
- Severe pain within a joint. For septic arthritis in the hip, pain may be referred to the buttock, thigh, or knee
- Swollen and/or hot joint
- Decreased movement of the joint
- A noticeable limp
- Other common symptoms consistent with a bacterial infection, such as fever, cold sweats, chills, extreme tiredness, and lack of appetite. In infants, irritability may be a symptom of septic arthritis.
(Click Septic Arthritis Symptoms to learn more about symptoms of septic arthritis, including which joints tend to be affected.)
There is no one specific test that can be used for diagnosing septic arthritis. Therefore, in order to make a diagnosis of septic arthritis, the healthcare provider will usually ask a number of questions, perform a physical exam, and recommend certain tests.
Tests that your healthcare provider may recommend include:
- X-rays or other imaging tests
- Synovial fluid testing
- Spinal tap.
Before making a diagnosis, the healthcare provider will also consider other conditions that share a number of symptoms with septic arthritis. Some of these conditions include:
Septic
arthritis treatment involves the use of antibiotics. The specific antibiotic recommended for the treatment of septic
arthritis will depend on the results of the synovial fluid analysis. Initially, antibiotics are given intravenously (through an IV). After a period of time, the healthcare provider will often switch the patient to antibiotics taken by mouth.
The length of treatment with antibiotics will depend on the specific type of bacteria. Streptococcal arthritis can usually be cured with antibiotics in 10 to 14 days. Other types of bacteria may require three to six weeks of treatment.
Treatment for septic arthritis also involves draining the infected joint.
(Click Septic Arthritis Treatment to learn more about treating septic arthritis, including more information about how a joint is drained.)
What Is the Prognosis for Septic Arthritis?
With treatment, the prognosis for people with septic arthritis is usually good. The risk for a poor outcome may increase in cases involving:
- Septic arthritis in young children or infants
- Associated osteomyelitis (infection of bone)
- Failure to treat the condition within seven days of its onset
- Septic arthritis in the hip.
