It seems awfully long time to be dealing with it to have it "get worse" after the doctor? Has he been to a physical therapist? My husband had an arm problem and it took several months of physical therapy but they found/corrected the problem! Now he does exercises daily/religiously. My neck/shoulder thing was helped by physical therapy even though it mostly needed time. I got an MRI to make sure there wasn't anything wrong and there was a torn muscle (but should have caused the pain I was having) and a few little, common, to-be-expected-for-my-age arthritis things going on in my neck but the massage and "attention" were helpful to me too. Took about 3 months to go away completely though. Sometimes it would hurt after and sometimes it would be better, depended on "its" mood :-)

I think knees are tricky things though; good luck to him!