What happens to you if there is an infection in the knee joint under the capsule?

Unsure? By your quesiton, I am unsure. However, if you believe you have an infections in your knee, anywhere, please see a doctor immediately and have it examined and appropriately treated. Knee infections are very serious and the sooner it is treated, the better. Don't delay. Get seen!
Severe arthritis. Infections in a joint space can be very serious because the joint space has minimal blood supply with limited ability to fight off the infection. Joint infections generally require surgery asap. Untreated the infection destroys the cartilage leading to chronic arthritic pain or worse.

Related Questions

How does a orthopedic know if there is an infection in the knee joint?

Suspicion/tests. The results of an exam & tests (cbc, crp, sed rate) often lead to suspicion about infection in a joint. A needle aspiration & lab examination of joint fluid is often the best way to be sure. Read more...
Aspiration. The best way is to get a sample of fluid from inside the knee joint and test it for white blood cells and send the fluid for a culture to see if a bacteria grows. Read more...
Symptoms. Symptoms and findings include redness, warmth, fevers, swelling and effusions, and pain with movement of knee, painful or enlarged lymph modes.....Ultimately proved be aspirating knee and looking under a microscope and growing cultures. Read more...

Is it possible to have an infection in or around a artificial knee joint for a couple years and it never be detected in blood work?

Unlikely. If you did not have fever, redness, pain and swelling of the knee, then it was not likely to be infected. You do not have infection that long without major problems developing long before 2 years. Read more...