Septic arthritis is an infection inside a joint that is caused by bacteria. (Septic describes an infection in the body caused by bacteria.) It comes on suddenly and causes very noticeable pain and swelling in the affected joint. It can affect anyone, including infants and children. But it is most likely to affect people over 60 and people with certain health or joint problems.
This guide will help you understand
- How septic arthritis develop
- How doctors diagnose the condition
- What can be done for septic arthritis
Where does septic arthritis develop?
About 80 percent of cases of septic arthritis involve only one joint. Roughly half of the time a knee is affected. The other most common sites are the hip, shoulder, wrist, ankle, elbow, and small joints in the hands and feet. When more than one joint is affected, the knees are usually involved.
Why do I have this problem?
Although they do not cause septic arthritis, several risk factors make it more likely to develop. These risk factors include a suppressed immune system, drug abuse, and other diseases. Other diseases that go along with septic arthritis include rheumatoid arthritis, diabetes, cancer, sickle cell disease, anemia, lupus, liver disease, skin infections, and hemophilia.
Artificial joints and recent joint surgery or arthrocentesis (inserting needles into the joint) are also risk factors for septic arthritis. However, the risk from these sources is small. The rate of septic arthritis from artificial joints is less than one percent. The rate following corticosteroid injections is less than 0.01 percent. Rates of septic arthritis following arthroscopy (surgery conducted using a small TV camera inserted into a joint) range from 0.04 percent to four percent. Septic arthritis caused by arthroscopy usually begins within two weeks of the procedure.
The biggest risk factor in septic arthritis is advanced age. Roughly half the cases of septic arthritis occur in people over age 60. In these patients, 75 percent of the infections occur in joints that have already been affected by arthritis, especially the hips, knees, and shoulders.
What does septic arthritis feel like?
How do doctors identify the condition?
If you have acute onset in one joint and a risk factor of any kind, your doctor will probably test for septic arthritis. A needle will be inserted into the joint and synovial fluid removed and sent to the lab. Your doctor will perform several tests on the synovial fluid. The most important test is probably the measuring the white blood cell count in the fluid. An infection in the joint causes the white blood cell count to be extremely high. Other tests are also useful especially making sure there are no crystals in the fluid that could indicate the presence of gout. A gout attack can easily be mistaken for an infection, and vice versa.
The fluid will be examined under a microscope to look for bacteria. Your doctor will also have the lab perform a culture of the synovial fluid to try and grow the bacteria. In this test a small sample of the fluid is placed in a special container and allowed to incubate in a warm cabinet. The test usually takes from 24 to 36 hours to see if any bacteria grow. This test can also help determine the specific type of bacteria that is causing the infection. If bacteria grow in culture the lab can also test different antibiotics on the bacteria to see which antibiotic will work the best.
Your doctor may ask you to have an X-ray. The X-ray will be used to look for any problems in the joint. It will also provide a baseline of information so your doctor can see the changes in your joint over the course of the infection.
What can be done for septic arthritis?
Antibiotics alone may not get rid of septic arthritis. The fluid in the joint may need to be drained at least once a day to remove the pus. This can be done using a large needle. In larger joints such as the knee, arthroscopy may also be used to wash the joint out and remove dead or damaged tissue. Surgery may be necessary to drain and clean joints such as the hip and shoulder. Surgery may also be necessary in joints with bone infections and in joints where the infection can’t be easily controlled.
As your infection begins to clear up, your doctor may suggest that you begin strengthening and range of motion exercises. They will help your joint regain its strength and flexibility. A physical or occupational therapist may oversee your exercise program.
How well your septic arthritis responds to treatment will depend on a number of factors. Most important is how soon you got treatment. Only about 25 percent of patients who wait a week to see a doctor can hope for a complete recovery. So you may feel as though your doctor is rushing you through tests and treatment, but it is for a very good reason.