Septic arthritis causes inflammation of a joint because of a bacterial infection. Septic arthritis is also known as infectious arthritis or bacterial arthritis.
Septic arthritis often affects the knees and hips, and may affect one joint or more than one at the same time.
What causes septic arthritis?
Septic arthritis can be caused by bacteria spreading from another area of the body. It can also be caused by a bacterial infection from an open wound, contaminated needle or an opening from a surgical procedure such as knee surgery.
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.
Who's at risk of septic arthritis?
Young children and elderly adults are most likely to develop septic arthritis. People with open wounds are also at a higher risk of 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 generalised weakness
- Low-grade fever
- 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 removed and sent to a laboratory for evaluation. The laboratory compares the white blood cell count with normal synovial fluid, and monitors 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 the inflammation. MRI scanning is sensitive in evaluating joint destruction. Blood tests can also be taken to detect and monitor inflammation.
What's the treatment for septic arthritis?
Septic arthritis treatments include using a combination of powerful antibiotics as well as draining the infected synovial fluid from the joint. It's likely that antibiotics will be administered immediately to avoid the spread of the infection. Intravenous (IV) antibiotics may be administered, which usually requires admission to hospital.
Initially empiric antibiotics are chosen to cover a wide range of infections. If the bacteria can be identified, antibiotics specific to that organism are used. It may take four to six weeks of treatment with antibiotics to ensure complete eradication of the infectious agents.