I recently developed a swollen, painful, stiff left knee, but have no history of trauma to the joint. any ideas for the cause?

Get evaluated: There could be many causes including arthritis and infections. You need to get evaluated to get correct diagnosis and treatment options.

Time 4 medical eval.: There are several possible causes of atraumatic knee swelling and pain. Inflammatory arthritis, degenerative arthritis, gout, and infection are a few of the possibilities. A visit to your physician should be able to give you an answer.