A:
You should see a doctor right away.
Your knee swelling could be due to hemarthrosis, which means bleeding into a joint. The most common cause is an injury. It can also occur in people who take blood thinners or whose blood does not clot well.
Most people with hemarthrosis have no fever. But blood in the joint can cause inflammation and that can occasionally cause a low grade fever.
Your injury could also have torn cartilage or ligaments or even created a fracture.
Other possible causes of knee swelling and fever include:
- Gout -- crystals of uric acid form in the joint
- Pseudogout -- calcium crystals form in the joint
- Infection -- bacteria or other microorganisms get into the joint through the blood or skin; an infection seems unlikely given your description of your injury
Because each of these can be associated with fever, I doubt that its a coincidence that you developed a fever just after your injury.
The best way to identify the cause of your joint swelling and fever is to have a sample of joint fluid removed and tested for the presence of crystals and infection. In addition, routine testing would determine the number of red blood cells (which can indicate bleeding) and white blood cells (which can indicate inflammation or infection).
Your doctor may advise one of these treatments. An anti-inflammatory such as ibuprofen (Advil, Motrin, or others) can reduce pain, inflammation and fever, but it may cause more bleeding. Acetaminophen (Tylenol or generics) may be a better choice, at least until the cause is determined. Other treatments depend on the results of additional testing, and may include a cortisone injection or antibiotics.
