Septic arthritis is also known as infectious arthritis or bacterial arthritis. The condition is an inflammation of a joint that's caused by infection. Typically, septic arthritis affects one large joint in the body, such as the knee or hip. However, septic arthritis can also affect multiple joints if the infection rapidly spreads.
What Causes Septic Arthritis?
Septic arthritis can be caused by bacteria that spreads from another area of the body. It can also be caused by a bacterial infection from an open wound or an opening from a surgical procedure, such as knee surgery.
In adults and children, common bacteria that cause acute septic arthritis include Haemophilus influenza, staphylococcus, and streptococcus. These foreign invaders enter the bloodstream and infect the joint, causing inflammation and pain.
Other infections, such as those caused by viruses and fungi, can also cause arthritis. Viruses include:
- hepatitis A, B, and C
- parvovirus B19
- herpes viruses
- HIV (AIDS virus)
- coxsackie viruses
Fungi that can cause arthritis include histoplasma, coccidiomyces, and blastomyces. These infections are usually less severe and slower to develop than septic arthritis.
Who's at Risk for Septic Arthritis?
Young children and elderly adults are most likely to develop septic arthritis. People with open wounds are also at a higher risk for septic arthritis. In addition, people with a weakened immune system and those with pre-existing conditions such as cancer, diabetes, intravenous drug abuse, and rheumatic and immune deficiency disorders have a higher risk of septic arthritis.
What Are the Symptoms of Septic Arthritis?
Symptoms of septic arthritis usually come on rapidly with intense pain, joint swelling, and fever. Septic arthritis symptoms may include:
- fatigue and generalized weakness
- inability to move the limb with the infected joint
- severe pain in the affected joint, especially with movement
- swelling (increased fluid within the joint)
- warmth (the joint is red and warm to touch because of increased blood flow)
How Is Septic Arthritis Diagnosed?
A procedure called arthrocentesis is commonly used to make an accurate diagnosis of septic arthritis. This procedure involves a surgical puncture of the joint to draw a sample of the joint fluid, known as synovial fluid. Normally, this fluid is sterile and acts as a lubricant.
In arthrocentesis, a needle is inserted into the affected joint. Fluid from the joint is collected in the needle and sent to a lab for evaluation. The lab compares the white blood cell count with normal synovial fluid, and watches the fluid for any bacterial growth. This will help the doctor determine if an infection is present, and which organism is causing it.
X-rays, MRIs, and blood tests can also be used to monitor inflammation. MRI scanning is sensitive in evaluating joint destruction. Blood tests can also be taken to detect and monitor inflammation.