Several months ago, I was in the gym doing some back squats and felt a twinge in my right knee. I figured it was my form (which is horrible). I racked the bar, readjusted, and plowed through the rest of my workout (always a bad idea).
The next day, my knee was swollen and painful to walk on. I gave it a couple of days, and it felt a little better but I still wanted to get checked out. I asked around and found a reputable, local orthopedic doctor. He performed a clinical exam and stated that I probably have a medial meniscal tear.