I had to cut short my leg workout today because of a weird pain in my right knee.

The pain originates on the medial side of my patella and seems to radiate up and down from the joint slightly. The pain goes away if I maintain greater than 135 degrees of flexion in the knee joint and the pain increases sharply if I approach or exceed 90 degrees, especially when under additional weight (I noticed it when I was doing a warmup set of squats).

I had just finished sets of leg extensions and leg curls with no problem when this thing reared its ugly head. I'll have my favourite chiropractor check it out tomorrow, but in the meantime does anyone have any advice/observations/ideas about what might cause pain like that?

I don't recall any major trauma to the knee in recent memory, though I did prang it a bit playing football at the beach yesterday.