I just had my knee examined...
with what sounds like the exact same symptoms. I figured it was a meniscal tear on the medial left knee, which is my front foot knee. I went to an orthopedist after 6weeks in pain. With only Xrays and physical tests he determined I had no tear, but pain from overuse on a normally degenerative posterior medial meniscus for my age of 41 and activity level.
I was pretty set on getting a 2nd opinion and/or MRI because it was just killing me- limping most of the time, no way I could run or ride. So my wife throws out going gluten free for a week to see if it helped. A friend of ours swears it rid his knees of arthritic pain. I think American pussy, fad, alergen diets are terrible, but... after two days of zero gluten my knee feels at least 60-70% better.
Could be just coincidence. But it's the first day my knee has begun to feel better in almost 2 months. Gluten free beer sucks though. The only thing I've found that's OK so far is Omission Pale Ale at $10 a six pack.