Step 4: Read and complete the decision guide to learn more about your symptoms.
Based on your answers (you are older than 45, no other joints are bothering you other than your knee, your painful knee is swollen and there is locking and/or giving way of the knee), there are a number of possible causes of knee pain. More than one may be present at the same time, including:
cartilage damage and/or ligament damage
crystal-induced disease such as gout and pseudogout
infection (less likely).