I think we are on the same page here RichM. Your body is adaptable and cells renew in order to cope with the demands placed upon them. The areas of the body with the best blood supply renew quickest and the muscles which support a knee joint are definitely in this category. There is a small amount of tissue within a knee joint which is really not supplied with blood and hence not very good at replacing/strengthening. These are for the attentions of a surgeon, everything else is a case of challenge the tissue provoke the adaptation.
I don't think you should be doing anything before knowing, what’s the problem with your knee. Everything concerning to joints and related shouldn't be taken lightly. I am a victim of such a stupidity. I had issues with my shoulder, was bit dislocated but I thought it's OK and I asked suggestions of others without figuring out my problem. I worsen the situation and I had to bear the pain for another 8 months and sometimes I can't stop my tears. I was assisted by a PT (Dynamic Physiotherapy & Sports Injury Clinic Ontario) for few months, got a relief from the pain, then he recommended me some exercises and that kept me feel better. Now I'm back to working out and keeping myself fit. You have to figure out what's your situation, then find a good assistance who can teach you exercise that you can continue till you are better.